Flexible, porous, dissolvable solid sheet articles having large pores and method of making same

ABSTRACT

This provides a flexible, porous, dissolvable solid sheet article having large pores on its top surface as well as a method of making the same.

FIELD OF THE INVENTION

The present invention relates to flexible, porous, dissolvable solidsheet articles having large pores on their top surfaces as well as amethod of making the same.

BACKGROUND OF THE INVENTION

Flexible dissolvable sheets comprising surfactant(s) and/or other activeingredients in a water-soluble polymeric carrier or matrix are wellknown. Such sheets are particularly useful for delivering surfactantsand/or other active ingredients upon dissolution in water. In comparisonwith traditional granular or liquid forms in the same product category,such sheets have better structural integrity, are more concentrated andeasier to store, ship/transport, carry, and handle. In comparison withthe solid tablet form in the same product category, such sheets are moreflexible and less brittle, with better sensory appeal to the consumers.

In order to deliver a sufficient amount of surfactant(s) and/or otheractive ingredients to achieve the desired product function, it isdesirable to use multiple layers of such flexible and dissolvablesheets, and it is further desirable to assemble such multiple layersinto a unitary dissolvable solid article, which can then be sold as aunitary finished product. However, various challenges may be encounteredwhen trying to assemble multiple layers of these flexible anddissolvable sheets into a unitary article, including significantlyslower dissolution rate in water, in comparison with a single layerstructure.

To improve dissolution, some studies has developed porous sheets withopen-celled foam (OCF) structures characterized by a Percent Open CellContent of from about 80% to 100%. Particularly, WO2010077627 disclosesa batch process for forming such porous sheets with OCF structures thatcomprises vigorously aerating a pre-mixture of raw materials and thenallowing the aerated pre-mixture to be heat-dried in batches (e.g., in aconvection oven or a microwave oven) to form the porous sheets with thedesired OCF structures. WO2012138820 discloses a similar process as thatof WO2010077627, except that continuous drying of the aerated wetpre-mixture is achieved by using, e.g., an impingement oven (instead ofa convection oven or a microwave oven). Although such OCF structures inthese studies significantly improve the dissolution rate of theresulting porous sheets, there is still a visibly denser and less porousregion (i.e., at the top surface) with thicker cell walls in suchsheets. Such high-density region may negatively impact the flow of waterthrough the sheets and thereby may adversely affect the overalldissolution rate of the sheets.

There is therefore a continuing need for improving pore structures inflexible, porous, dissolvable sheets and enhancing dissolution profilethereof.

SUMMARY OF THE INVENTION

The present invention provides a flexible, porous, dissolvable sheethaving a further improved pore structure, especially at the top surfaceas well as a method for making such sheet. Particularly, prior to thepresent invention, it was believed that air bubbles in the aeratedpre-mixture might gradually collapse over time, and thereby long-termstorage of the aerated pre-mixture might adversely affect the porestructures in the sheets as well as dissolution profile of the sheets.As such, it was suggested that the aerated pre-mixture was immediatelydried after the aerating step. Surprisingly, inventors of the presentinvention have unexpectedly discovered that the introduction of an agingstep (i.e., maintaining the aerated pre-mixture for a while afterstopping the aerating) before the drying step may bring about asignificantly improved pore structures and thereby a significantlyimproved dissolution profile. As such, the present inventors havesuccessfully prepared a flexible, porous, dissolvable sheet having afurther improved pore structure that has not been obtained prior to thepresent invention.

In one aspect, the present invention relates to a process for making asheet article, comprising the steps of: a) preparing a wet pre-mixturecomprising a water-soluble polymer and a surfactant and having aviscosity of from about 1,000 cps to about 25,000 cps measured at 40° C.and 1 s⁻¹; b) aerating the wet pre-mixture to form an aerated wetpre-mixture having a density of from about 0.05 to about 0.5 g/ml; c)aging the aerated wet pre-mixture for at least about 5 minute; d)forming the aerated wet pre-mixture into a sheet having opposing firstand second sides; and e) drying the formed sheet for a drying time offrom about 1 minute to about 60 minutes to make the sheet article.Preferably, the step c) may be conducted for a duration from about 5 minto about 300 min, preferably from about 5 min to about 200 min, morepreferably from about 10 min to about 150 min, for example 5 min, 6 min,7 min, 8 min, 9 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40min, 45 min, 50 min, 55 min, 60 min, 70 min, 80 min, 90 min, 100 min,110 min, 120 min, 130 min, 140 min or any ranges therebetween.Preferably, the drying in the step e) may be conducted at a temperaturefrom about 70° C. to about 200° C. along a heating direction that formsa temperature gradient decreasing from the first side to the second sideof the formed sheet, wherein the heating direction is substantiallyopposite to the gravitational direction for more than half of the dryingtime.

The sheet formed by the aerated wet pre-mixture may be dried on a heatedsurface that preferably has a controlled surface temperature of fromabout 70° C. to about 170° C., preferably from about 75° C. to about150° C., more preferably from about 80° C. to about 120° C. Preferably,the heated surface may be a primary heat source for the sheet duringdrying. More preferably, the heated surface may be the only heat sourcefor the sheet during drying.

Particularly, the heated surface may be the outer surface of a rotarydrum dryer that preferably has an outer diameter ranging from about 0.5meters to about 10 meters, preferably from about 1 meter to about 5meters, more preferably from about 1.5 meters to about 2 meters and isrotated at a speed of from about 0.005 rpm to about 0.25 rpm, preferablyfrom about 0.05 rpm to about 0.2 rpm, more preferably from about 0.1 rpmto about 0.18 rpm, during the drying step. Alternatively, the heatedsurface may be the outer surface of a heated moving belt (for example, aconveyor belt) that is preferably moving at a speed of from about 0.1m/min to about 50 m/min, preferably from about 0.15 m/min to about 20m/min, more preferably from about 0.2 m/min to about 10 m/min, forexample, 0.1 m/min, 0.2 m/min, 0.3 m/min, 0.4 m/min, 0.5 m/min, 0.7m/min, 1 m/min, 2 m/min, 3 m/min, 5 m/min, 10 m/min, 15 m/min, 20 m/min,or any ranges therebetween, during the drying step.

Further, in the step d), the sheet may be formed by using a spinning barthat is rotating at a speed of from about 5 to about 80 rpm, preferablyfrom about 6 to about 60 rpm, more preferably from about 8 to about 50rpm, most preferably from about 10 to about 40 rpm. Preferably, thespinning bar may be positioned so that the distance between the spinningbar and the outer surface of the rotary drum or the heated moving beltis from about 3 mm to about 15 mm, preferably from about 4 mm to about12 mm, more preferably from about 5 mm to about 10 mm, most preferablyfrom about 6 mm to about 10 mm. Alternatively, in the step d), the sheetmay be formed by a feeding die having a feeding speed of from about 0.1m/min to about 50 m/min, preferably from about 0.15 m/min to about 20m/min, more preferably from about 0.2 m/min to about 10 m/min, forexample, 0.1 m/min, 0.2 m/min, 0.3 m/min, 0.4 m/min, 0.5 m/min, 0.7m/min, 1 m/min, 2 m/min, 3 m/min, 5 m/min, 10 m/min, 15 m/min, 20 m/min,or any ranges therebetween. Preferbaly, the feeding die may have afeeding thickness of from 0.5 mm to 10 mm, preferably from 1 mm to 6 mm,more preferably from 1.5 mm to 4 mm. Preferably, the feeding die may bepositioned so that the distance between the feeding die and the outersurface of the rotary drum or the heated moving belt is from about 0.1mm to about 15 mm, preferably from about 0.2 mm to about 12 mm, morepreferably from about 0.3 mm to about 10 mm, most preferably from about0.5 mm to about 5 mm.

Still further, the wet pre-mixture may be characterized by: (1) a solidcontent ranging from about 15% to about 70%, preferably from about 20%to about 50%, more preferably from about 25% to about 45% by weight ofthe wet pre-mixture; and (2) a viscosity ranging from about 3,000 cps toabout 24,000 cps, preferably from about 5,000 cps to about 23,000 cps,more preferably from about 10,000 cps to about 20,000 cps as measured at40° C. and 1 s⁻¹.

Still further, the wet pre-mixture may be preheated to a temperature offrom about 40° C. to about 100° C., preferably from about 50° C. toabout 95° C., more preferably from about 60° C. to about 90° C., mostpreferably from about 75° C. to about 85° C., before aeration; and/orthe wet pre-mixture may be maintained at a temperature of from about 40°C. to about 100° C., preferably from about 50° C. to about 95° C., morepreferably from about 60° C. to about 90° C., most preferably from about75° C. to about 85° C., during aeration; and/or the aerated wetpre-mixture may be maintained at a temperature of from about 10° C. toabout 100° C., preferably from about 15° C. to about 70° C., morepreferably from about 20° C. to about 50° C., most preferably from about20° C. to about 40° C. in the step c).

Still further, the drying time may be from about 2 to about 30 minutes,preferably from about 2 to about 25 minutes, more preferably from about2 to about 20 minutes, most preferably from about 2 to about 15 minutes;and/or wherein the drying temperature is from about 80° C. to about 170°C., preferably from about 90° C. to about 150° C., more preferably fromabout 100° C. to about 140° C.; and the heating direction may besubstantially opposite to the gravitational direction for more thanabout 55%, preferably more than about 60%, more preferably more thanabout 75% of the drying time.

Still further, the aerating in the step b) may be accomplished byintroducing a gas into the wet pre-mixture by using a mechanicalprocessing means, including but not limited to: a rotor stator mixer, aplanetary mixer, a pressurized mixer, a non-pressurized mixer, a batchmixer, a continuous mixer, a semi-continuous mixer, a high shear mixer,a low shear mixer, a submerged sparger, or any combinations thereof.

In another aspect, the present invention provides a flexible, porous,dissolvable solid sheet article comprising a water-soluble polymer and asurfactant, wherein the solid sheet article is characterized by: (i) athickness ranging from 0.5 mm to 4 mm; and (ii) a Percent Open CellContent of from 80% to 100%; and (iii) an Overall Average Pore Size offrom 100 μm to 2000 μm; wherein the solid sheet article has opposing topand bottom surfaces, the top surface having a Surface Average PoreDiameter that is greater than about 300 μm. Particularly, the topsurface may have a Surface Average Pore Diameter that is from about 300μm to about 2 mm, preferably from about 350 μm to about 1.5 mm, morepreferably from about 400 μm to about 1 mm.

The solid sheet article may comprise a top region adjacent to the topsurface, a bottom region adjacent to the bottom surface, and a middleregion therebetween; wherein the top, middle, and bottom regions havethe same thickness, and each of the top, middle and bottom regions ischaracterized by an Average Pore Size. Particularly, the ratio ofAverage Pore Size in the bottom region over that in the top region maybe from about 0.6 to about 1.5, preferably from about 0.7 to about 1.4,more preferably from about 0.8 to about 1.3, most preferably from about1 to about 1.2; and/or the ratio of Average Pore Size in the bottomregion over that in the middle region may be from about 0.5 to about1.5, preferably from about 0.6 to about 1.3, more preferably from about0.8 to about 1.2, most preferably from about 0.9 to about 1.1; and/orthe ratio of Average Pore Size in the middle region over that in the topregion may be from about 1 to about 1.5, preferably from about 1 toabout 1.4, more preferably from about 1 to about 1.2.

The solid sheet article may comprise from about 5% to about 40%,preferably from about 8% to about 30%, more preferably from about 10% toabout 25%, of the water-soluble polymer by total weight of the solidsheet article. Preferably, the water-soluble polymer may have a weightaverage molecular weight of from about 5,000 to about 400,000 Daltons,more preferably from about 10,000 to about 300,000 Daltons, still morepreferably from about 15,000 to about 200,000 Daltons, most preferablyfrom about 20,000 to about 150,000 Daltons. More preferably, thewater-soluble polymer may comprise a first water-soluble polymer havinga first weight average molecular weight and a second water-solublepolymer having a second weight average molecular weight, in which thefirst weight average molecular weight may be from about 5,000 to about50,000 Daltons, more preferably from about 10,000 to about 40,000Daltons, still more preferably from about 15,000 to about 35,000Daltons, most preferably from about 20,000 to about 30,000 Daltons;and/or the second weight average molecular weight may be from about20,000 to about 400,000 Daltons, more preferably from about 30,000 toabout 300,000 Daltons, still more preferably from about 40,000 to about200,000 Daltons, most preferably from about 50,000 to about 150,000Daltons. Preferably, the water-soluble polymer may be a polyvinylalcohol characterized by a degree of hydrolysis ranging from about 40%to about 100%, preferably from about 50% to about 95%, more preferablyfrom about 65% to about 92%, most preferably from about 70% to about90%.

The solid sheet article may comprise from 5% to 80%, preferably from 10%to 70%, more preferably from 30% to 65%, of the surfactant by totalweight of the solid sheet article. Preferably, the surfactant may beselected from the group consisting of: anionic surfactants, non-ionicsurfactants, cationic surfactants, zwitterionic surfactants, amphotericsurfactants, polymeric surfactants and any combinations thereof.

Further, the solid sheet article may further comprise from 0.1% to 25%,preferably from 0.5% to 20%, more preferably from 1% to 15%, mostpreferably from 2% to 12%, of a plasticizer by total weight of the solidsheet article. Preferably, the plasticizer may be selected from thegroup consisting of glycerin, ethylene glycol, polyethylene glycol,propylene glycol, and combinations thereof. More preferably, theplasticizer may be glycerin.

Still further, the solid sheet article may contain one or moreadditional ingredients, such as fabric care actives, dishwashingactives, hard surface cleaning actives, beauty and/or skin care actives,personal cleansing actives, hair care actives, oral care actives,feminine care actives, baby care actives, and any combinations thereof.

The flexible, porous, dissolvable solid sheet article of the presentinvention may further be characterized by:

-   -   a Percent Open Cell Content of from about 85% to 100%,        preferably from about 90% to 100%; and/or    -   an Overall Average Pore Size of from about 150 μm to about 1000        μm, preferably from about 200 μm to about 600 μm; and/or    -   an Average Cell Wall Thickness of from about 5 μm to about 200        μm, preferably from about 10 μm to about 100 μm, more preferably        from about 10 μm to about 80 μm; and/or    -   a final moisture content of from about 0.5% to about 25%,        preferably from about 1% to about 20%, more preferably from        about 3% to about 10%, by weight of the solid sheet article;        and/or    -   a thickness ranging from about 0.6 mm to about 3.5 mm,        preferably from about 0.7 mm to about 3 mm, more preferably from        about 0.8 mm to about 2 mm, most preferably from about 1 mm to        about 1.5 mm; and/or    -   a basis weight of from about 50 grams/m² to about 250 grams/m²,        preferably from about 80 grams/m² to about 220 grams/m², more        preferably from about 100 grams/m² to about 200 grams/m²; and/or    -   a density of from about 0.05 grams/cm³ to about 0.5 grams/cm³,        preferably from about 0.06 grams/cm³ to about 0.4 grams/cm³,        more preferably from about 0.07 grams/cm³ to about 0.2        grams/cm³, most preferably from about 0.08 grams/cm³ to about        0.15 grams/cm³; and/or    -   a Specific Surface Area of from about 0.03 m²/g to about 0.25        m²/g, preferably from about 0.04 m²/g to 0.22 m²/g, more        preferably from about 0.05 m²/g to about 0.2 m²/g, most        preferably from about 0.1 m²/g to about 0.18 m²/g.

These and other aspects of the present invention will become moreapparent upon reading the following detailed description of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art convection-based heating/drying arrangement formaking a flexible, porous, dissolvable solid sheet article in a batchprocess.

FIG. 2 shows a prior art microwave-based heating/drying arrangement formaking a flexible, porous, dissolvable solid sheet article in a batchprocess.

FIG. 3 shows a prior art impingement oven-based heating/dryingarrangement for making a flexible, porous dissolvable solid sheetarticle in a continuous process.

FIG. 4 shows a bottom conduction-based heating/drying arrangement formaking an flexible, porous, dissolvable sheet in a batch process,according to one embodiment of the present invention.

FIG. 5 shows a rotary drum-based heating/drying arrangement for makinganother flexible, porous, dissolvable sheet in a continuous process,according to another embodiment of the present invention.

FIG. 6A shows a Scanning Electron Microscopic (SEM) image of the topsurface of a flexible, porous, dissolvable sheet containing fabric careactives, which is made by a process employing a rotary drum-basedheating/drying arrangement. FIG. 6B shows a SEM image of the top surfaceof a flexible, porous, dissolvable sheet containing the same fabric careactives as the sheet shown in FIG. 6A, but which is made by a processemploying an impingement oven-based heating/drying arrangement.

FIG. 7A shows a SEM image of the top surface of a flexible, porous,dissolvable sheet containing hair care actives, which is made by aprocess employing a bottom conduction-based heating/drying arrangement.FIG. 7B shows a SEM image of the top surface of a flexible, porous,dissolvable sheet containing the same hair care actives as the sheetshown in FIG. 7A, but which is made by a process employing animpingement oven-based heating/drying arrangement.

FIG. 8A shows a photo of bubbles in the wet pre-mixture after a 70-minaging step. FIG. 8B shows a photo of bubbles in the wet pre-mixturebefore the 70-min aging step (i.e., immediately after an aeration step).

FIG. 9A shows a photo of bubbles in the wet pre-mixture after a 120-minaging step in a drum drying process. FIG. 9B shows a photo of bubbles inthe wet pre-mixture having the same formulation as that shown in FIG. 9Awithout an aging step after aeration in a drum drying process.

FIG. 10A shows a SEM image of the top surface of Article 1 (an inventiveflexible, porous, dissolvable sheet article having large pores on itstop surface) in Example 3. FIG. 10B shows a SEM image of the top surfaceof Article 2 (a comparative flexible, porous, dissolvable sheet articlehaving relatively small pores on its top surface) in Example 3.

FIG. 11 shows the dissolution profiles over time in the dissolution testfor Articles 1 and 2 in Example 3, in which Article 1 showssignificantly improved dissolution profile compared to Article 2.

FIG. 12A shows a SEM image of the top surface of Article 3 (an inventiveflexible, porous, dissolvable sheet article having large pores on itstop surface) in Example 4. FIG. 12B shows a SEM image of the top surfaceof Article 4 (a comparative flexible, porous, dissolvable sheet articlehaving relatively small pores on its top surface) in Example 4.

FIG. 13A shows a SEM image of the top surface of Article 5 (an inventiveflexible, porous, dissolvable sheet article having large pores on itstop surface) in Example 5. FIG. 13B shows a SEM image of the top surfaceof Article 6 (a comparative flexible, porous, dissolvable sheet articlehaving relatively small pores on its top surface) in Example 5.

FIG. 14 shows the dissolution profiles over time in the dissolution testfor Articles 5 and 6 in Example 5, in which Article 5 showssignificantly improved dissolution profile compared to Article 6.

DETAILED DESCRIPTION OF THE INVENTION I. Definitions

The term “flexible” as used herein refers to the ability of an articleto withstand stress without breakage or significant fracture when it isbent at 90° along a center line perpendicular to its longitudinaldirection. Preferably, such article can undergo significant elasticdeformation and is characterized by a Young's Modulus of no more than 5GPa, preferably no more than 1 GPa, more preferably no more than 0.5GPa, most preferably no more than 0.2 GPa.

The term “dissolvable” as used herein refers to the ability of anarticle to completely or substantially dissolve in a sufficient amountof deionized water at 20° C. and under the atmospheric pressure withineight (8) hours without any stirring, leaving less than 5 wt %undissolved residues.

The term “solid” as used herein refers to the ability of an article tosubstantially retain its shape (i.e., without any visible change in itsshape) at 20° C. and under the atmospheric pressure, when it is notconfined and when no external force is applied thereto.

The term “sheet” as used herein refers to a non-fibrous structure havinga three-dimensional shape, i.e., with a thickness, a length, and awidth, while the length-to-thickness aspect ratio and thewidth-to-thickness aspect ratio are both at least about 5:1, and thelength-to-width ratio is at least about 1:1. Preferably, thelength-to-thickness aspect ratio and the width-to-thickness aspect ratioare both at least about 10:1, more preferably at least about 15:1, mostpreferably at least about 20:1; and the length-to-width aspect ratio ispreferably at least about 1.2:1, more preferably at least about 1.5:1,most preferably at least about 1.618:1.

As used herein, the term “bottom surface” refers to a surface of theflexible, porous, dissolvable solid sheet article of the presentinvention that is immediately contacting a supporting surface upon whichthe sheet of aerated wet pre-mixture is placed during the drying step,while the term “top surface” refers to a surface of the sheet articlethat is opposite to the bottom surface. Further, such solid sheetarticle can be divided into three (3) regions along its thickness,including a top region that is adjacent to its top surface, a bottomregion that is adjacent to its bottom surface, and a middle region thatis located between the top and bottom regions. The top, middle, andbottom regions are of equal thickness, i.e., each having a thicknessthat is about ⅓ of the total thickness of the sheet article.

The term “open celled foam” or “open cell pore structure” as used hereinrefers to a solid, interconnected, polymer-containing matrix thatdefines a network of spaces or cells that contain a gas, typically a gas(such as air), without collapse of the foam structure during the dryingprocess, thereby maintaining the physical strength and cohesiveness ofthe solid. The interconnectivity of the structure may be described by aPercent Open Cell Content, which is measured by Test 3 disclosedhereinafter.

The term “water-soluble” as used herein refers to the ability of asample material to completely dissolve in or disperse into water leavingno visible solids or forming no visibly separate phase, when at leastabout 25 grams, preferably at least about 50 grams, more preferably atleast about 100 grams, most preferably at least about 200 grams, of suchmaterial is placed in one liter (1 L) of deionized water at 20° C. andunder the atmospheric pressure with sufficient stirring.

The term “aerate”, “aerating” or “aeration” as used herein refers to aprocess of introducing a gas into a liquid or pasty composition bymechanical and/or chemical means.

The term “heating direction” as used herein refers to the directionalong which a heat source applies thermal energy to an article, whichresults in a temperature gradient in such article that decreases fromone side of such article to the other side. For example, if a heatsource located at one side of the article applies thermal energy to thearticle to generate a temperature gradient that decreases from the oneside to an opposing side, the heating direction is then deemed asextending from the one side to the opposing side. If both sides of sucharticle, or different sections of such article, are heatedsimultaneously with no observable temperature gradient across sucharticle, then the heating is carried out in a non-directional manner,and there is no heating direction.

The term “substantially opposite to” or “substantially offset from” asused herein refers to two directions or two lines having an offset angleof 90° or more therebetween.

The term “substantially aligned” or “substantial alignment” as usedherein refers to two directions or two lines having an offset angle ofless than 90° therebetween.

The term “primary heat source” as used herein refers to a heat sourcethat provides more than 50%, preferably more than 60%, more preferablymore than 70%, most preferably more than 80%, of the total thermalenergy absorbed by an object (e.g., the sheet of aerated wet pre-mixtureaccording to the present invention).

The term “controlled surface temperature” as used herein refers to asurface temperature that is relatively consistent, i.e., with less than+/−20% fluctuations, preferably less than +/−10% fluctuations, morepreferably less than +/−5% fluctuations.

The term “age” or “aging” as used herein refers to a process ofmaintaining an aerated wet mixture or pre-mixture for a while withoutfurther introducing a significant amount of gas. Preferably, the agingmay be conducted under the conditions of being essentially free ofmechanical energy input and/or being essentially free of heat input.More preferably, the aging may be conducted under the ambienttemperature without any stirring.

The term “essentially free of” or “essentially free from” means that theindicated material is at the very minimal not deliberately added to thecomposition or product, or preferably not present at an analyticallydetectible level in such composition or product. It may includecompositions or products in which the indicated material is present onlyas an impurity of one or more of the materials deliberately added tosuch compositions or products.

II. Overview of Processes for Making Solid Sheet Articles

WO2010077627 discloses a batch process for forming porous sheets withopen-celled foam (OCF) structures characterized by a Percent Open CellContent of from about 80% to 100%, which functions to improvedissolution. Specifically, a pre-mixture of raw materials is firstformed, which is vigorously aerated and then heat-dried in batches(e.g., in a convection oven or a microwave oven) to form the poroussheets with the desired OCF structures. Although such OCF structuressignificantly improve the dissolution rate of the resulting poroussheets, there is still a visibly denser and less porous bottom regionwith thicker cell walls in such sheets. Such high-density bottom regionmay negatively impact the flow of water through the sheets and therebymay adversely affect the overall dissolution rate of the sheets. When aplurality of such sheets is stacked together to form a multilayerstructure, the “barrier” effect of multiple high-density bottom regionsis especially augmented.

WO2012138820 discloses a similar process as that of WO2010077627, exceptthat continuous drying of the aerated wet pre-mixture is achieved byusing, e.g., an impingement oven (instead of a convection oven or amicrowave oven). The OCF sheets formed by such a continuous dryingprocess are characterized by improved uniformity/consistency in the porestructures across different regions thereof. Unfortunately, there arestill rate-limiting factors in such OCF sheets, such as a top surfacewith relatively smaller pore openings and a top region with relativelysmaller pores (i.e., a crust-like top region), which may negativelyimpact the flow of water therethrough and slow down the dissolutionthereof.

During the drying step in the above-described processes, the OCFstructures are formed under simultaneous mechanisms of waterevaporation, bubble collapse, interstitial liquid drainage from the thinfilm bubble facings into the plateau borders between the bubbles (whichgenerates openings between the bubbles and forms the open cells), andsolidification of the pre-mixture. Various processing conditions mayinfluence these mechanisms, e.g., solid content in the wet pre-mixture,viscosity of the wet pre-mixture, gravity, and the drying temperature,and the need to balance such processing conditions so as to achievecontrolled drainage and form the desired OCF structures.

It has been a surprising and unexpected discovery of the presentinvention that the direction of thermal energy employed (i.e., theheating direction) during the drying step may also have a significantimpact on the resulting OCF structures, in addition to theabove-mentioned processing conditions.

For example, if the thermal energy is applied in a non-directionalmatter (i.e., there is no clear heating direction) during the dryingstep, or if the heating direction is substantially aligned with thegravitational direction (i.e., with an offset angle of less than 90° inbetween) during most of the drying step, the resulting flexible, porous,dissolvable solid sheet tends to have a top surface with smaller poreopenings and greater pore size variations in different regions along thedirection across its thickness. In contrast, when the heating directionis offset from the gravitation direction (i.e., with an offset angle of90° or more therebetween) during most of the drying step, the resultingsolid sheet may have a top surface with larger pore openings and reducedpore size variations in different regions along the direction across thethickness of such sheet. Correspondingly, the latter sheets are morereceptive to water flowing through and are therefore more dissolvablethan the former sheets.

While not being bound by any theory, it is believed that the alignmentor misalignment between the heating direction and the gravitationaldirection during the drying step and the duration thereof maysignificantly affect the interstitial liquid drainage between thebubbles, and correspondingly impacting the pore expansion and poreopening in the solidifying pre-mixture and resulting in solid sheetswith very different OCF structures. Such differences are illustratedmore clearly by FIGS. 1-4 hereinafter.

FIG. 1 shows a convection-based heating/drying arrangement. During thedrying step, a mold 10 (which can be made of any suitable materials,such as metal, ceramic or Teflon®) is filled with an aerated wetpre-mixture, which forms a sheet 12 having a first side 12A (i.e., thetop side) and an opposing second side 12B (i.e., the bottom side sinceit is in direct contact with a supporting surface of the mold 10). Suchmold 10 is placed in a 130° C. convection oven for approximately 45-46minutes during the drying step. The convection oven heats the sheet 12from above, i.e., along a downward heating direction (as shown by thecross-hatched arrowhead), which forms a temperature gradient in thesheet 12 that decreases from the first side 12A to the opposing secondside 12B. The downward heating direction is aligned with gravitationaldirection (as shown by the white arrowhead), and such an alignedposition is maintained throughout the entire drying time. During drying,gravity drains the liquid pre-mixture downward toward the bottom region,while the downward heating direction dries the top region first and thebottom region last. As a result, a porous solid sheet is formed with atop surface that contains numerous pores with small openings formed bygas bubbles that have not had the chance to fully expand. Such a topsurface with smaller pore openings is not optimal for water ingress intothe sheet, which may limit the dissolution rate of the sheet. On theother hand, the bottom region of such sheet is dense and less porous,with larger pores that are formed by fully expanded gas bubbles, butwhich are very few in numbers, and the cell walls between the pores insuch bottom region are thick due to the downward liquid drainageeffectuated by gravity. Such a dense bottom region with fewer pores andthick cell walls is a further rate-limiting factor for the overalldissolution rate of the sheet.

FIG. 2 shows a microwave-based heating/drying arrangement. During thedrying step, a mold 30 is filled with an aerated wet pre-mixture, whichforms a sheet 32 having a first side 32A (the top side) and an opposingsecond side 32B (the bottom side). Such mold 30 is then placed in a lowenergy density microwave applicator (not shown), which is provided byIndustrial Microwave System Inc., North Carolina and operated at a powerof 2.0 kW, a belt speed of 1 foot per minute and a surrounding airtemperature of 54.4° C. The mold 30 is placed in such microwaveapplication for approximately 12 minutes during the drying step. Suchmicrowave applicator heats the sheet 32 from within, without any clearor consistent heating direction. Correspondingly, no temperaturegradient is formed in the sheet 32. During drying, the entire sheet 32is simultaneously heated, or nearly simultaneously heated, althoughgravity (as shown by the white arrowhead) still drains the liquidpre-mixture downward toward the bottom region. As a result, thesolidified sheet so formed has more uniformly distributed and moreevenly sized pores, in comparison with sheet formed by theconvection-based heating/drying arrangement. However, the liquiddrainage under gravity force during the microwave-based drying step maystill result in a dense bottom region with thick cell walls. Further,simultaneous heating of the entire sheet 32 may still limit the poreexpansion and pore opening on the top surface during the drying step,and the resulting sheet may still have a top surface with relativelysmaller pore openings. Further, the microwave energy heats water withinthe sheet 32 and causes such water to boil, which may generate bubblesof irregular sizes and form unintended dense regions with thick cellwalls.

FIG. 3 shows an impingement oven-based heating/drying arrangement.During the drying step, a mold 40 is filled with an aerated wetpre-mixture, which forms a sheet 42 having a first side 42A (the topside) and an opposing second side 42B (the bottom side). Such mold 40 isthen placed in a continuous impingement oven (not shown) underconditions similar to those described in Example 1, Table 2 ofWO2012138820. Such continuous impingement oven heats the sheet 42 fromboth top and bottom at opposing and offsetting heating directions (shownby the two cross-hatched arrowheads). Correspondingly, no cleartemperature gradient is formed in the sheet 42 during drying, and theentire sheet 42 is nearly simultaneously heated from both its top andbottom surfaces. Similar to the microwave-based heating/dryingarrangement described in FIG. 3, gravity (as shown by the whitearrowhead) continues to drain the liquid pre-mixture downward toward thebottom region in such impingement oven-based heating/drying arrangementof FIG. 4. As a result, the solidified sheet so formed has moreuniformly distributed and more evenly sized pores, in comparison withsheet formed by the convection-based heating/drying arrangement.However, the liquid drainage under gravity force during the drying stepmay still result in a dense bottom region with thick cell walls.Further, nearly simultaneous heating of the sheet 42 from both the maystill limit the pore expansion and pore opening on the top surfaceduring the drying step, and the resulting sheet may still have a topsurface with relatively smaller pore openings.

In contrast to the above-described heating/drying arrangements(convection-based, microwave-based or impingement oven-based), thepresent invention provides a heating/drying arrangement for drying theaerated wet pre-mixture, in which the direction of heating ispurposefully configured to counteract/reduce liquid drainage caused bythe gravitational force toward the bottom region (thereby reducing thedensity and improving pore structures in the bottom region) and to allowmore time for the air bubbles near the top surface to expand duringdrying (thereby forming significantly larger pore openings on the topsurface of the resulting sheet). Both features function to improveoverall dissolution rate of the sheet and are therefore desirable.

FIG. 4 shows a bottom conduction-based heating/drying arrangement formaking a flexible, porous, dissolvable sheet, according to oneembodiment of the present invention. Specifically, a mold 50 is filledwith an aerated wet pre-mixture, which forms a sheet 52 having a firstside 52A (i.e., the bottom side) and an opposing second side 52B (i.e.,the top side). Such mold 50 is placed on a heated surface (not shown),for example, on top of a pre-heated Peltier plate with a controlledsurface temperature of about 125-130° C., for approximately 30 minutesduring the drying step. Heat is conducted from the heated surface at thebottom of the mold 50 through the mold to heat the sheet 52 from below,i.e., along an upward heating direction (as shown by the cross-hatchedarrowhead), which forms a temperature gradient in the sheet 52 thatdecreases from the first side 52A (the bottom side) to the opposingsecond side 52B (the top side). Such an upward heating direction isopposite to the gravitational direction (as shown by the whitearrowhead), and it is maintained as so throughout the entire drying time(i.e., the heating direction is opposite to the gravitational directionfor almost 100% of the drying time). During drying, the gravitationalforce still drains the liquid pre-mixture downward toward the bottomregion. However, the upward heating direction dries the sheet frombottom up, and water vapor generated by heat at the bottom region arisesupward to escape from the solidifying matrix, so the downward liquiddrainage toward the bottom region is significantly limited and“counteracted”/reduced by the solidifying matrix and the uprising watervapor. Correspondingly, the bottom region of the resulting dry sheet isless dense and contains numerous pores with relatively thin cell walls.Further, because the top region is the last region that is dried duringthis process, the air bubbles in the top region have sufficient time toexpand to form significantly larger open pores at the top surface of theresulting sheet, which are particularly effective in facilitating wateringress into the sheet. Moreover, the resulting sheet has a more evenlydistributed overall pore sizes throughout different regions (e.g., top,middle, bottom) thereof.

FIG. 5 shows a rotary drum-based heating/drying arrangement for making aflexible, porous, dissolvable sheet, according to another embodiment ofthe present invention. Specifically, a feeding trough 60 is filled withan aerated wet pre-mixture 61. A heated rotatable cylinder 70 (alsoreferred to as a drum dryer) is placed above the feeding trough 60. Theheated drum dryer 70 has a cylindrical heated outer surfacecharacterized by a controlled surface temperature of about 130° C., andit rotates along a clock-wise direction (as shown by the thin curvedline with an arrowhead) to pick up the aerated wet pre-mixture 61 fromthe feeding trough 60. The aerated wet pre-mixture 61 forms a thin sheet62 over the cylindrical heated outer surface of the drum dryer 70, whichrotates and dries such sheet 62 of aerated wet pre-mixture inapproximately 10-15 minutes. A leveling blade (not shown) may be placednear the slurry pick-up location to ensure a consistent thickness of thesheet 62 so formed, although it is possible to control the thickness ofsheet 62 simply by modulating the viscosity of the aerated wetpre-mixture 61 and the rotating speed and surface temperature of thedrum dryer 70. Once dried, the sheet 62 can then picked up, eithermanually or by a scraper 72 at the end of the drum rotation.

As shown in FIG. 5, the sheet 62 formed by the aerated wet pre-mixture61 comprises a first side 62A (i.e., the bottom side) that directlycontacts the heated outer surface of the heated drum dryer 70 and anopposing second side 62B (i.e., the top side). Correspondingly, heatfrom the drum dryer 70 is conducted to the sheet 62 along an outwardheating direction, to heat the first side 62A (the bottom side) of thesheet 62 first and then the opposing second side 62B (the top side).Such outward heating direction forms a temperature gradient in the sheet62 that decreases from the first side 62A (the bottom side) to theopposing second side 62B (the top side). The outward heating directionis slowly and constantly changing as the drum dryer 70 rotates, butalong a very clear and predictable path (as shown by the multipleoutwardly extending cross-hatched arrowheads in FIG. 4). The relativeposition of the outward heating direction and the gravitationaldirection (as shown by the white arrowhead) is also slowing andconstantly changing in a similar clear and predictable manner. For lessthan half of the drying time (i.e., when the heating direction is belowthe horizontal dashed line), the outward heating direction issubstantially aligned with the gravitational direction with an offsetangle of less than 90° in between. During majority of the drying time(i.e., when the heating direction is flushed with or above thehorizontal dashed line), the outward heating direction is opposite orsubstantially opposite to the gravitational direction with an offsetangle of 90° or more therebetween. Depending on the initial “start”coating position of the sheet 62, the heating direction can be oppositeor substantially opposite to the gravitational direction for more than55% of the drying time (if the coating starts at the very bottom of thedrum dryer 70), preferably more than 60% of the drying time (if thecoating starts at a higher position of the drum dryer 70, as shown inFIG. 5). Consequently, during most of the drying step this slowingrotating and changing heating direction in the rotary drum-basedheating/drying arrangement can still function to limit and“counteract”/reduce the liquid drainage in sheet 62 caused by thegravitational force, resulting in improved OCF structures in the sheetso formed. The resulting sheet as dried by the heated drum dryer 70 isalso characterized by a less dense bottom region with numerous moreevenly sized pores, and a top surface with relatively larger poreopenings. Moreover, the resulting sheet has a more evenly distributedoverall pore sizes throughout different regions (e.g., top, middle,bottom) thereof.

In addition to employing the desired heating direction (i.e., in asubstantially offset relation with respect to the gravitationaldirection) as mentioned hereinabove, it may also be desirable and evenimportant to carefully adjust the viscosity and/or solid content of thewet pre-mixture, the amount and speed of aeration (air feed pump speed,mixing head speed, air flow rate, density of the aerated pre-mixture andthe like, which may affect bubble sizes and quantities in the aeratedpre-mixture and correspondingly impact the poresize/distribution/quantity/characteristics in the solidified sheet), thedrying temperature and the drying time, in order to achieve optimal OCFstructure in the resulting sheet according to the present invention.

Furthermore, it has been a surprising and unexpected discovery of thepresent invention that the introduction of an aging step (i.e.,maintaining the aerated pre-mixture for a while after stopping theaerating) before the drying step may bring about an even furtherimproved pore structures and thereby a further improved dissolutionprofile. Prior to the present invention, it was believed that airbubbles in the aerated wet pre-mixture might gradually collapse as timepasses by, and thereby long-term storage of the aerated wet pre-mixturemight adversely affect the pore structures in the sheets as well asdissolution profile of the sheets. As such, it was suggested that theaerated pre-mixture was immediately dried after the aerating step.Surprisingly, inventors of the present invention have unexpectedlydiscovered that, although the air bubbles in the aerated wet pre-mixtureindeed gradually collapse after long-term storage (for example, 6-8hours), an aging step for an appropriate time period (for example, lessthan 5 hours) would benefit to the pore structure, especially pores atthe top surface. Particularly, the introduction of an aging step beforethe drying step may provide larger pores at the top surface of theflexible, porous, dissolvable sheet compared to the sheets obtained by aprocess without such aging step.

More detailed descriptions of the processes for making the flexible,porous, dissolvable sheets according to the present invention, as wellas the physical and chemical characteristics of such sheets, areprovided in the ensuring sections.

III. Inventive Process of Making Solid Sheet Articles

The present invention provides a new and improved method for makingflexible, porous, dissolvable solid sheet articles, which comprises thesteps of: (a) forming a pre-mixture containing raw materials (e.g., thewater-soluble polymer, active ingredients such as surfactants, andoptionally a plasticizer) dissolved or dispersed in water or a suitablesolvent, which is characterized by a viscosity of from about 1,000 cpsto about 25,000 cps measured at about 40° C. and 1 s⁻¹; (b) aeratingsaid pre-mixture (e.g., by introducing a gas into the wet slurry) toform an aerated wet pre-mixture; (c) aging the aerated wet pre-mixturefor at least 5 min; (d) forming the aerated wet pre-mixture into a sheethaving opposing first and second sides; and (e) drying the formed sheetfor a drying time of from 1 minute to 60 minutes at a temperature from70° C. to 200° C. along a heating direction that forms a temperaturegradient decreasing from the first side to the second side of saidformed sheet, wherein the heating direction is substantially offset fromthe gravitational direction for more than half of the drying time, i.e.,the drying step is conducted under heating along a mostly “anti-gravity”heating direction. Such a mostly “anti-gravity” heating direction can beachieved by various means, which include but are not limited to thebottom conduction-based heating/drying arrangement and the rotarydrum-based heating/drying arrangement, as illustrated hereinabove inFIGS. 4 and 5 respectively.

Step (A): Preparation of Wet Pre-Mixture

The wet pre-mixture of the present invention is generally prepared bymixing solids of interest, including the water-soluble polymer,surfactant(s) and/or other benefit agents, optional plasticizer, andother optional ingredients, with a sufficient amount of water or anothersolvent in a pre-mix tank. The wet pre-mixture can be formed using amechanical mixer. Mechanical mixers useful herein, include, but aren'tlimited to pitched blade turbines or MAXBLEND mixer (Sumitomo HeavyIndustries).

It is particularly important in the present invention to adjustviscosity of the wet pre-mixture so that it is within a predeterminedrange of from about 1,000 cps to about 25,000 cps when measured at 40°C. and 1 s⁻¹. Viscosity of the wet pre-mixture has a significant impacton the pore expansion and pore opening of the aerated pre-mixture duringthe subsequent drying step, and wet pre-mixtures with differentviscosities may form flexible, porous, dissolvable solid sheet articlesof very different foam structures. On one hand, when the wet pre-mixtureis too thick/viscous (e.g., having a viscosity higher than about 25,000cps as measured at 40° C. and 1 s⁻¹), aeration of such wet pre-mixturemay become more difficult. More importantly, interstitial liquiddrainage from thin film bubble facings into the plateau borders of thethree-dimensional foam during the subsequent drying step may beadversely affected or significantly limited. The interstitial liquiddrainage during drying is believed to be critical for enabling poreexpansion and pore opening in the aerated wet pre-mixture during thesubsequent drying step. As a result, the flexible, porous, dissolvablesolid sheet article so formed thereby may have significantly smallerpores and less interconnectivity between the pores (i.e., more “closed”pores than open pores), which render it harder for water to ingress intoand egress from such sheet article. On the other hand, when the wetpre-mixture is too thin/running (e.g., having a viscosity lower thanabout 1,000 cps as measured at 40° C. and 1 s⁻¹), the aerated wetpre-mixture may not be sufficiently stable, i.e., the air bubbles mayrupture, collapse, or coalescence too quickly in the wet pre-mixtureafter aeration and before drying. Consequently, the resulting solidsheet article may be much less porous and more dense than desired.

Particularly, viscosity of the wet pre-mixture ranges from about 3,000cps to about 24,000 cps, preferably from about 5,000 cps to about 23,000cps, more preferably from about 10,000 cps to about 20,000 cps, asmeasured at 40° C. and 1 sec⁻¹. The pre-mixture viscosity values aremeasured using a Malvern Kinexus Lab+ rheometer with cone and plategeometry (CP1/50 SR3468 SS), a gap width of 0.054 mm, a temperature of40° C. and a shear rate of 1.0 reciprocal seconds for a period of 360seconds.

Preferably, the solids of interest are present in the wet pre-mixture ata level of from about 15% to about 70%, preferably from about 20% toabout 50%, more preferably from about 25% to about 45% by total weightof said wet pre-mixture. The percent solid content is the summation ofthe weight percentages by weight of the total processing mixture of allsolid components, semi-solid components and liquid components excludingwater and any obviously volatile materials such as low boiling alcohols.On one hand, if the solid content in the wet pre-mixture is too high,viscosity of the wet pre-mixture may increase to a level that willprohibit or adversely affect interstitial liquid drainage and preventformation of the desired predominantly open-celled porous solidstructure as described herein. On the other hand, if the solid contentin the wet pre-mixture is too low, viscosity of the wet pre-mixture maydecrease to a level that will cause bubble rupture/collapse/coalescenceand more percent (%) shrinkage of the pore structures during drying,resulting in a solid sheet article that is significantly less porous anddenser.

Among the solids of interest in the wet pre-mixture of the presentinvention, there may be present from about 1% to about 75%surfactant(s), from about 0.1% to about 25% water-soluble polymer, andoptionally from about 0.1% to about 25% plasticizer, by total weight ofthe solids. Other actives or benefit agents can also be added into thepre-mixture.

Optionally, the wet pre-mixture is pre-heated immediately prior toand/or during the aeration process at above ambient temperature butbelow any temperatures that would cause degradation of the componentstherein. In one embodiment, the wet pre-mixture is kept at an elevatedtemperature ranging from about 40° C. to about 100° C., preferably fromabout 50° C. to about 95° C., more preferably from about 60° C. to about90° C., most preferably from about 75° C. to about 85° C. In oneembodiment, the optional continuous heating is utilized before theaeration step. Further, additional heat can be applied during theaeration process to try and maintain the wet pre-mixture at such anelevated temperature. This can be accomplished via conductive heatingfrom one or more surfaces, injection of steam or other processing means.It is believed that the act of pre-heating the wet pre-mixture beforeand/or during the aeration step may provide a means for lowering theviscosity of pre-mixtures comprising higher percent solids content forimproved introduction of bubbles into the mixture and formation of thedesired solid sheet article. Achieving higher percent solids content isdesirable since it may reduce the overall energy requirements fordrying. The increase of percent solids may therefore conversely lead toa decrease in water level content and an increase in viscosity. Asmentioned hereinabove, wet pre-mixtures with viscosities that are toohigh are undesirable for the practice of the present invention.Pre-heating may effectively counteract such viscosity increase and thusallow for the manufacture of a fast dissolving sheet article even whenusing high solid content pre-mixtures.

Step (B): Aeration of Wet Pre-Mixture

Aeration of the wet pre-mixture is conducted in order to introduce asufficient amount of air bubbles into the wet pre-mixture for subsequentformation of the OCF structures therein upon drying. Once sufficientlyaerated, the wet pre-mixture is characterized by a density that issignificantly lower than that of the non-aerated wet pre-mixture (whichmay contain a few inadvertently trapped air bubbles) or aninsufficiently aerated wet pre-mixture (which may contain some bubblesbut at a much lower volume percentage and of significantly larger bubblesizes). Preferably, the aerated wet pre-mixture has a density rangingfrom about 0.05 g/ml to about 0.5 g/ml, preferably from about 0.08 g/mlto about 0.4 g/ml, more preferably from about 0.1 g/ml to about 0.35g/ml, still more preferably from about 0.15 g/ml to about 0.3 g/ml, mostpreferably from about 0.2 g/ml to about 0.25 g/ml.

Aeration can be accomplished by either physical or chemical means in thepresent invention. In one embodiment, it can be accomplished byintroducing a gas into the wet pre-mixture through mechanical agitation,for example, by using any suitable mechanical processing means,including but not limited to: a rotor stator mixer, a planetary mixer, apressurized mixer, a non-pressurized mixer, a batch mixer, a continuousmixer, a semi-continuous mixer, a high shear mixer, a low shear mixer, asubmerged sparger, or any combinations thereof. In another embodiment,it may be achieved via chemical means, for example, by using chemicalfoaming agents to provide in-situ gas formation via chemical reaction ofone or more ingredients, including formation of carbon dioxide (CO₂ gas)by an effervescent system.

In a particularly preferred embodiment, it has been discovered that theaeration of the wet pre-mixture can be cost-effectively achieved byusing a continuous pressurized aerator or mixer that is conventionallyutilized in the foods industry in the production of marshmallows.Continuous pressurized mixers may work to homogenize or aerate the wetpre-mixture to produce highly uniform and stable foam structures withuniform bubble sizes. The unique design of the high shear rotor/statormixing head may lead to uniform bubble sizes in the layers of the opencelled foam. Suitable continuous pressurized aerators or mixers includethe Morton whisk (Morton Machine Co., Motherwell, Scotland), the Oakescontinuous automatic mixer (E.T. Oakes Corporation, Hauppauge, N.Y.),the Fedco Continuous Mixer (The Peerless Group, Sidney, Ohio), the Mondo(Haas-Mondomix B.V., Netherlands), the Aeros (Aeros Industrial EquipmentCo., Ltd., Guangdong Province, China), and the Preswhip (Hosokawa MicronGroup, Osaka, Japan). For example, an Aeros A20 continuous aerator canbe operated at a feed pump speed setting of about 300-800 (preferably atabout 500-700) with a mixing head speed setting of about 300-800(preferably at about 400-600) and an air flow rate of about 50-150(preferably 60-130, more preferably 80-120) respectively. For anotherexample, an Oakes continuous automatic mixer can be operated at a mixinghead speed setting of about 10-30 rpm (preferably about 15-25 rpm, morepreferably about 20 rpm) with an air flow rate of about 10-30 Litres perhour (preferably about 15-25 L/hour, more preferably about 19-20L/hour).

As mentioned hereinabove, the wet pre-mixture can be maintained at anelevated temperature during the aeration process, so as to adjustviscosity of the wet pre-mixture for optimized aeration and controlleddraining during drying.

Bubble size of the aerated wet pre-mixture assists in achieving uniformlayers in the OCF structures of the resulting solid sheet article. Inone embodiment, the bubble size of the aerated wet pre-mixture is fromabout 5 to about 200 microns; and in another embodiment, the bubble sizeis from about 20 microns to about 100 microns. Uniformity of the bubblesizes causes the resulting solid sheet articles to have consistentdensities.

Step (C): Aging

After sufficient aeration, the aerated wet pre-mixture is maintained fora while without further introducing a significant amount of air. Suchaging step may be conducted in any suitable manners. For example, theaerated wet pre-mixture may be stored in a container such as a bucket ora tank without any stirring. For another example, the aerated wetpre-mixture may be stirred by using a spinning bar to prevent phaseseparation or sedimentation, in which the rotating speed of the spinningbar is preferably low enough (for example, from about 5 to about 80 rpm)to prevent introduction further air and/or high shear force in theaerated wet pre-mixture. Without being bound by any theory, it isbelieved that high shear force in the aerated wet pre-mixture mightcompromise the further expansion of bubbles or even reduce bubblesinstead.

Particularly, the aging may be conducted for a duration from 5 min to300 min, preferably from 5 min to 200 min, more preferably from 10 minto 150 min. As mentioned hereinabove, the wet pre-mixture may bemaintained at ambient temperature or at an elevated temperature duringthe aging step, for example from 10° C. to 100° C., preferably from 15°C. to 70° C., more preferably from 20° C. to 50° C., most preferablyfrom 20° C. to 40° C.

Step (D): Sheet-Forming

After aging, the aged wet pre-mixture forms one or more sheets withopposing first and second sides. The sheet-forming step can be conductedin any suitable manners, e.g., by extrusion, casting, molding,vacuum-forming, pressing, printing, coating, and the like. Morespecifically, the aerated wet pre-mixture can be formed into a sheet by:(i) casting it into shallow cavities or trays or specially designedsheet moulds; (ii) extruding it onto a continuous belt or screen of adryer; or (iii) coating it onto the outer surface of a rotary drumdryer. Preferably, the supporting surface upon which the sheet is formedis formed by or coated with materials that are anti-corrosion,non-interacting and/or non-sticking, such as metal (e.g., steel,chromium, and the like), TEFLON®, polycarbonate, NEOPRENE®, HDPE, LDPE,rubber, glass and the like.

Preferably, the formed sheet of aerated wet pre-mixture has a thicknessranging from a thickness ranging from 0.5 mm to 4 mm, preferably from0.6 mm to 3.5 mm, more preferably from 0.7 mm to 3 mm, still morepreferably from 0.8 mm to 2 mm, most preferably from 0.9 mm to 1.5 mm.Controlling the thickness of such formed sheet of aerated wetpre-mixture may be important for ensuring that the resulting solid sheetarticle has the desired OCF structures. If the formed sheet is too thin(e.g., less than 0.5 mm in thickness), many of the air bubbles trappedin the aerated wet pre-mixture will expand during the subsequent dryingstep to form through-holes that extend through the entire thickness ofthe resulting solid sheet article. Such through-holes, if too many, maysignificantly compromise both the overall structural integrity andaesthetic appearance of the sheet article. If the formed sheet is toothick, not only it will take longer to dry, but also it will result in asolid sheet article with greater pore size variations between differentregions (e.g., top, middle, and bottom regions) along its thickness,because the longer the drying time, the more imbalance of forces mayoccur through bubble rupture/collapse/coalescence, liquid drainage, poreexpansion, pore opening, water evaporation, and the like. Further,multiple layers of relatively thin sheets can be assembled intothree-dimensional structures of greater thickness to deliver the desiredcleaning benefits or other benefits, while still providing satisfactorypore structures for fast dissolution as well as ensuring efficientdrying within a relatively short drying time.

Step (E): Drying Under Anti-Gravity Heating

A key feature of the present invention is the use of an anti-gravityheating direction during the drying step, either through the entiredrying time or at least through more than half of the drying time.Without being bound by any theory, it is believed that such anti-gravityheating direction may reduce or counteract excessive interstitial liquiddrainage toward the bottom region of the formed sheet during the dryingstep. Further, because the top surface is dried last, it allows longertime for air bubbles near the top surface of the formed sheet to expandand form pore openings on the top surface (because once the wet matrixis dried, the air bubbles can no longer expand or form surfaceopenings). Consequently, the solid sheet formed by drying with suchanti-gravity heating is characterized by improved OCF structures thatenables faster dissolution as well as other surprising and unexpectedbenefits.

In a specific embodiment, the anti-gravity heating direction is providedby a conduction-based heating/drying arrangement, either the same orsimilar to that illustrated by FIG. 4. For example, the aerated wetpre-mixture can be casted into a mold to form a sheet with two opposingsides. The mold can then be placed on a hot plate or a heated movingbelt (for example, a heated conveyor belt) or any other suitable heatingdevice with a planar heated surface characterized by a controlledsurface temperature of from about 80° C. to about 170° C., preferablyfrom about 90° C. to about 150° C., more preferably from about 100° C.to about 140° C. Alternatively, the aerated wet pre-mixture can beapplied onto the outer surface of a heated moving belt such as aconveyor belt to form a sheet with two opposing sides. Thermal energy istransferred from the planar heated surface to the bottom surface of thesheet of aerated wet pre-mixture via conduction, so that solidificationof the sheet starts with the bottom region and gradually moves upward toreach the top region last. In order to ensure that the heating directionis primarily anti-gravity (i.e., substantially offset from thegravitational direction) during this process, it is preferred that theheated surface is a primary heat source for the sheet during drying. Ifthere are any other heating sources, the overall heating direction maychange accordingly. More preferably, the heated surface is the only heatsource for the sheet during drying. And, if a heated moving belt isemployed, it is preferred that the aerated wet pre-mixture is appliedonto the outer surface of the moving belt when the outer surface of themoving belt is upward or is changing from downward to upward. Oncedried, the sheet may be picked up, either manually or by a scraper,preferably when the outer surface of the moving belt is still upward oris changing from upward to downward. Preferably, the moving belt maymove at a speed of from about 0.1 m/min to about 50 m/min, preferablyfrom about 0.15 m/min to about 20 m/min, more preferably from about 0.2m/min to about 10 m/min, during the drying step.

In another specific embodiment, the anti-gravity heating direction isprovided by a rotary drum-based heating/drying arrangement, which isalso referred to as drum drying or roller drying, similar to thatillustrated in FIG. 5. Drum drying is one type of contact-dryingmethods, which is used for drying out liquids from a viscous pre-mixtureof raw materials over the outer surface of a heated rotatable drum (alsoreferred to as a roller or cylinder) at relatively low temperatures toform sheet-like articles. It is a continuous drying process particularlysuitable for drying large volumes. Because the drying is conducted atrelatively low temperatures via contact-heating/drying, it normally hashigh energy efficiency and does not adversely affect the compositionalintegrity of the raw materials. The heated rotatable cylinder used indrum drying is heated internally, e.g., by steam or electricity, and itis rotated by a motorized drive installed on a base bracket at apredetermined rotational speed. The heated rotatable cylinder or drumpreferably has an outer diameter ranging from about 0.5 meters to about10 meters, preferably from about 1 meter to about 5 meters, morepreferably from about 1.5 meters to about 2 meters. It may have acontrolled surface temperature of from about 80° C. to about 170° C.,preferably from about 90° C. to about 150° C., more preferably fromabout 100° C. to about 140° C. Further, such heated rotatable cylinderis rotating at a speed of from about 0.005 rpm to about 0.25 rpm,preferably from about 0.05 rpm to about 0.2 rpm, more preferably fromabout 0.1 rpm to about 0.18 rpm. The heated rotatable cylinder ispreferably coated with a non-stick coating on its outer surface. Thenon-stick coating may be overlying on the outer surface of the heatedrotatable drum, or it can be fixed to a medium of the outer surface ofthe heated rotatable drum. The medium includes, but is not limited to,heat-resisting non-woven fabrics, heat-resisting carbon fiber,heat-resisting metal or non-metallic mesh and the like. The non-stickcoating can effectively preserve structural integrity of the sheet-likearticle from damage during the sheet-forming process.

In order to form a sheet on a heated surface (for example, the outersurface of a rotary drum dryer or a heated moving belt), a feedingmechanism may be provided, independently or as a part of the dryingdevice (for example, the rotary drum dryer or the heated moving belt).Such feeding mechanism is employed to apply the aerated wet pre-mixtureof raw materials as described hereinabove onto the heated surface,thereby forming a thin layer of the viscous pre-mixture onto the heatedsurface. Such thin layer of the pre-mixture is therefore dried by theheated surface via contact-heating/drying. The feeding mechanism mayinclude a feeding hopper, a feeding die, an extruder, or a spinning barthrough which the aerated wet pre-mixture is applied onto the heatedsurface. The feeding mechanism may further include a feeding trough thatis employed for containing the wet aerated pre-mixture, an imagingdevice for dynamic observation of the feeding, and/or an adjustmentdevice for adjusting the position and/or inclination angle of thefeeding hopper, the feeding die, the extruder or the spinning bar.

In a preferred but not necessary embodiment, a spinning bar is employedfor applying the aerated wet pre-mixture. Preferably, the spinning barmay be rotating at a speed of from 5 to 80 rpm, preferably from 6 to 60rpm, more preferably from 8 to 50 rpm, most preferably from 10 to 40rpm. Also preferably, the spinning bar may be positioned so that thedistance between the spinning bar and the outer surface of the rotarydrum or the heated moving belt is from 3 mm to 15 mm, preferably from 4mm to 12 mm, more preferably from 5 mm to 10 mm, most preferably from 6mm to 10 mm. Without being bound by any theory, it is believed that ifan appropriate rotating speed and/or an appropriate distance between thespinning bar the outer surface of the rotary drum or the heated movingbelt are used, it would not introduce further air bubbles and/or causehigh shear force that may compromise the formation of large bubbles. Assuch, it may result in an even larger bubble size of pre-mixture fedonto the heated surface and in turn, an improved pore structure in theformed sheet.

In another preferred but not necessary embodiment, a feeding die isemployed for applying the aerated wet pre-mixture. Preferably, thefeeding die may have a feeding speed of from about 0.1 m/min to about 50m/min, preferably from about 0.15 m/min to about 20 m/min, morepreferably from about 0.2 m/min to about 10 m/min. Also preferably, thefeeding die may be positioned so that the distance between the feedingdie and the outer surface of the rotary drum or the heating moving beltis from 0.1 mm to 15 mm, preferably from 0.2 mm to 12 mm, morepreferably from 0.3 mm to 10 mm, most preferably from 0.5 mm to 5 mm.Without being bound by any theory, it is believed that if an appropriatefeeding speed and/or an appropriate distance between the feeding die andthe outer surface of the rotary drum or the heated moving belt are used,it may achieve a preferred sheet formation and/or an even larger bubblesize.

There may also be a heating shield that is preferably installed on thebase bracket, to prevent rapid heat lost. The heating shield can alsoeffectively save energy needed by the heated surface, thereby achievingreduced energy consumption and provide cost savings. The heating shieldis a modular assembly structure, or integrated structure, and can befreely detached from the base bracket. A suction device is alsoinstalled on the heating shield for sucking the hot steam, to avoid anywater condensate falling on the sheet-like article that is being formed.

There may also be an optional static scraping mechanism that ispreferably installed on the base bracket, for scraping or scooping upthe sheet-like article already formed by the heated surface. The staticscraping mechanism can be installed on the base bracket, or on one sidethereof, for transporting the already formed sheet-like articledownstream for further processing. The static scraping mechanism canautomatically or manually move close and go away from the heatedrotatable drum.

Preferably, the making process of the flexible, porous, dissolvablesolid sheet of the present invention may be as follows. Firstly, theheated rotatable drum with the non-stick coating on the base bracket isdriven by the motorized drive. Next, the adjustment device adjusts thefeeding mechanism so that the distance between the feeding hopper andthe outer surface of the heated rotatable drum reaches a preset value.Meanwhile, the feeding hopper adds the aerated wet pre-mixturecontaining all or some raw materials for making the flexible, porous,dissolvable solid sheet onto an outer surface of the heated rotatabledrum, to form a thin layer of the aerated wet pre-mixture thereon withthe desired thickness as described hereinabove in the preceding section.Optionally, the suction device of the heating shield sucks the hot steamgenerated by the heated rotatable drum. Next, the static scrapingmechanism scrapes/scoops up a dried/solidified sheet, which is formed bythe thin layer of aerated wet pre-mixture after it is dried by theheated rotatable drum at a relatively low temperature (e.g., 130° C.).The dried/solidified sheet can also be manually or automatically peeledoff, without such static scraping mechanism and then rolled up by aroller bar.

The total drying time in the present invention depends on theformulations and solid contents in the wet pre-mixture, the dryingtemperature, the thermal energy influx, and the thickness of the sheetmaterial to be dried. Preferably, the drying time is from about 1 minuteto about 60 minutes, preferably from about 2 minutes to about 30minutes, more preferably from about 2 to about 15 minutes, still morepreferably from about 2 to about 10 minutes, most preferably from about2 to about 5 minutes, for example, 3 min, 5 min, 7 min, 10 min, 15 min,20 min, 25 min, 30 min or any ranges therebetween.

During such drying time, the heating direction is so arranged that it issubstantially opposite to the gravitational direction for more than halfof the drying time, preferably for more than 55% or 60% of the dryingtime (e.g., as in the rotary drum-based heating/drying arrangementdescribed hereinabove), more preferably for more than 75% or even 100%of the drying time (e.g., as in the bottom conduction-basedheating/drying arrangement described hereinabove). Further, the sheet ofaerated wet pre-mixture can be dried under a first heating direction fora first duration and then under a second, opposite heating directionunder a second duration, while the first heating direction issubstantially opposite to the gravitational direction, and while thefirst duration is anywhere from 51% to 99% (e.g., from 55%, 60%, 65%,70% to 80%, 85%, 90% or 95%) of the total drying time. Such change inheating direction can be readily achieved by various other arrangementsnot illustrated herein, e.g., by an elongated heated belt of aserpentine shape that can rotate along a longitudinal central axis.

IV. Physical Characteristics of Inventive Solid Sheet Articles

The flexible, porous, dissolvable solid sheet article formed by theabove-described processing steps is characterized by improved porestructures that allows easier water ingress into the sheet article andfaster dissolution of the sheet article in water. Such improved porestructures are achieved mainly by adjusting various processingconditions as described hereinabove, and they are relatively independentor less influenced by the chemical formulations or the specificingredients used for making such sheet article.

In general, such solid sheet article may be characterized by: (i) aPercent Open Cell Content of from about 80% to 100%, preferably fromabout 85% to 100%, more preferably from about 90% to 100%, as measuredby the Test 3 hereinafter; and (ii) an Overall Average Pore Size of fromabout 100 μm to about 2000 μm, preferably from about 150 μm to about1000 μm, more preferably from about 200 μm to about 600 μm, as measuredby the Micro-CT method described in Test 2 hereinafter. The OverallAverage Pore Size defines the porosity of the OCF structure of thepresent invention. The Percent Open Cell Content defines theinterconnectivity between pores in the OCF structure of the presentinvention. Interconnectivity of the OCF structure may also be describedby a Star Volume or a Structure Model Index (SMI) as disclosed inWO2010077627 and WO2012138820.

Such solid sheet article of the present invention has opposing top andbottom surfaces, while its top surface may be characterized by a SurfaceAverage Pore Diameter that is greater than about 300 μm, preferablygreater than about 310 μm, preferably greater than about 320 μm, morepreferably greater than about 330 μm, most preferably greater than about350 μm, as measured by the SEM method described in Test 1 hereinafter.When comparing with solid sheet articles formed by prior artheating/drying arrangements (e.g., the convection-based, themicrowave-based, or the impingement oven-based arrangements), the solidsheet article formed by the inventive heating/drying arrangement of thepresent invention has a significantly larger Surface Average PoreDiameter at its top surface (as demonstrated by FIGS. 6A-6B, 7A-7B and8A-8B, which are described in detail in Example 1 hereinafter).

Still further, the solid sheet article formed by the inventiveheating/drying arrangement of the present invention is characterized bya more uniform pore size distribution between different regions alongits thickness direction, in comparison with the sheets formed by priorart heating/drying arrangements. Specifically, the solid sheet articleof the present invention comprises a top region adjacent to the topsurface, a bottom region adjacent to the bottom surface, and a middleregion therebetween, while the top, middle, and bottom regions all havethe same thickness. Each of the top, middle and bottom regions of suchsolid sheet article is characterized by an Average Pore Size, while theratio of Average Pore Size in the bottom region over that in the topregion (i.e., bottom-to-top Average Pore Size ratio) is from about 0.6to about 1.5, preferably from about 0.7 to about 1.4, preferably fromabout 0.8 to about 1.3, more preferably from about 1 to about 1.2. Incomparison, a solid sheet article formed by a prior art impingementoven-based heating/drying arrangement may have a bottom-to-top AveragePore Size ratio of more than 1.5, typically about 1.7-2.2 (asdemonstrated in Example 1 hereinafter). Moreover, the solid sheetarticle of the present invention may be characterized by abottom-to-middle Average Pore Size ratio of from about 0.5 to about 1.5,preferably from about 0.6 to about 1.3, more preferably from about 0.8to about 1.2, most preferably from about 0.9 to about 1.1, and amiddle-to-top Average Pore Size ratio of from about 1 to about 1.5,preferably from about 1 to about 1.4, more preferably from about 1 toabout 1.2.

Still further, the relative standard deviation (RSTD) between AveragePore Sizes in the top, middle and bottom regions of the solid sheetarticle of the present invention is no more than 20%, preferably no morethan 15%, more preferably no more than 10%, most preferably no more than5%. In contrast, a solid sheet article formed by a prior art impingementoven-based heating/drying arrangement may have a relative standarddeviation (RSTD) between top/middle/bottom Average Pore Sizes of morethan 20%, likely more than 25% or even more than 35%.

Preferably, the solid sheet article of the present invention is furthercharacterized by an Average Cell Wall Thickness of from about 5 μm toabout 200 μm, preferably from about 10 μm to about 100 μm, morepreferably from about 10 μm to about 80 μm, as measured by Test 2hereinafter.

The solid sheet article of the present invention may contain a smallamount of water. Preferably, it is characterized by a final moisturecontent of from 0.5% to 25%, preferably from 1% to 20%, more preferablyfrom 3% to 10%, by weight of said solid sheet article, as measured byTest 4 hereinafter. An appropriate final moisture content in theresulting solid sheet article may ensure the desiredflexibility/deformability of the sheet article, as well as providingsoft/smooth sensory feel to the consumers. If the final moisture contentis too low, the sheet article may be too brittle or rigid. If the finalmoisture content is too high, the sheet article may be too sticky, andits overall structural integrity may be compromised.

The solid sheet article of the present invention may have a thicknessranging from about 0.6 mm to about 3.5 mm, preferably from about 0.7 mmto about 3 mm, more preferably from about 0.8 mm to about 2 mm, mostpreferably from about 1 mm to about 1.5 mm. Thickness of the solid sheetarticle can be measured using Test 6 described hereinafter. The solidsheet article after drying may be slightly thicker than the sheet ofaerated wet pre-mixture, due to pore expansion that in turn leads tooverall volume expansion.

The solid sheet article of the present invention may further becharacterized by a basis weight of from about 50 grams/m² to about 250grams/m², preferably from about 80 grams/m² to about 220 grams/m², morepreferably from about 100 grams/m² to about 200 grams/m², as measured byTest 6 described hereinafter.

Still further, the solid sheet article of the present invention may havea density ranging from about 0.05 grams/cm³ to about 0.5 grams/cm³,preferably from about 0.06 grams/cm³ to about 0.4 grams/cm³, morepreferably from about 0.07 grams/cm³ to about 0.2 grams/cm³, mostpreferably from about 0.08 grams/cm³ to about 0.15 grams/cm³, asmeasured by Test 7 hereinafter. Density of the solid sheet article ofthe present invention is lower than that of the sheet of aerated wetpre-mixture, also due to pore expansion that in turn leads to overallvolume expansion.

Furthermore, the solid sheet article of the present invention can becharacterized by a Specific Surface Area of from about 0.03 m²/g toabout 0.25 m²/g, preferably from about 0.04 m²/g to about 0.22 m²/g,more preferably from 0.05 m²/g to 0.2 m²/g, most preferably from 0.1m²/g to 0.18 m²/g, as measured by Test 8 described hereinafter. TheSpecific Surface Area of the solid sheet article of the presentinvention may be indicative of its porosity and may impact itsdissolution rate, e.g., the greater the Specific Surface Area, the moreporous the sheet article and the faster its dissolution rate.

V. Formulations of Inventive Solid Sheet Articles

1. Water-Soluble Polymer

As mentioned hereinabove, the flexible, porous, dissolvable solid sheetarticle of the present invention may be formed by a wet pre-mixture thatcomprises a water-soluble polymer and a surfactant. Such a water-solublepolymer may function in the resulting solid sheet article as afilm-former, a structurant as well as a carrier for other activeingredients (e.g., surfactants, emulsifiers, builders, chelants,perfumes, colorants, and the like).

Preferably, the wet pre-mixture may comprise from about 3% to about 20%by weight of the pre-mixture of water soluble polymer, in one embodimentfrom about 5% to about 15% by weight of the pre-mixture of water solublepolymer, in one embodiment from about 7% to about 10% by weight of thepre-mixture of water soluble polymer.

After drying, it is preferred that the water-soluble polymer is presentin the flexible, porous, dissolvable solid sheet article of the presentinvention in an amount ranging from about 5% to about 40%, preferablyfrom about 8% to about 30%, more preferably from about 10% to about 25%,by total weight of the solid sheet article. In a particularly preferredembodiment of the present invention, the total amount of water-solublepolymer(s) present in the flexible, porous, dissolvable solid sheetarticle of the present invention is no more than 25% by total weight ofsuch article.

Water-soluble polymers suitable for the practice of the presentinvention may be selected those with weight average molecular weightsranging from about 5,000 to about 400,000 Daltons, more preferably fromabout 10,000 to about 300,000 Daltons, still more preferably from about15,000 to about 200,000 Daltons, most preferably from about 20,000 toabout 150,000 Daltons. The weight average molecular weight is computedby summing the average molecular weights of each polymer raw materialmultiplied by their respective relative weight percentages by weight ofthe total weight of polymers present within the porous solid. The weightaverage molecular weight of the water-soluble polymer used herein mayimpact the viscosity of the wet pre-mixture, which may in turn influencethe bubble number and size during the aeration step as well as the poreexpansion/opening results during the drying step. Further, the weightaverage molecular weight of the water-soluble polymer may affect theoverall film-forming properties of the wet pre-mixture and itscompatibility/incompatibility with certain surfactants.

The water-soluble polymers of the present invention may include, but arenot limited to, synthetic polymers including polyvinyl alcohols,polyvinylpyrrolidones, polyalkylene oxides, polyacrylates, caprolactams,polymethacrylates, polymethylmethacrylates, polyacryl amides,polymethylacrylamides, polydimethylacrylamides, polyethylene glycolmonomethacrylates, copolymers of acrylic acid and methyl acrylate,polyurethanes, polycarboxylic acids, polyvinyl acetates, polyesters,polyamides, polyamines, polyethyleneimines, maleic/(acrylate ormethacrylate) copolymers, copolymers of methylvinyl ether and of maleicanhydride, copolymers of vinyl acetate and crotonic acid, copolymers ofvinylpyrrolidone and of vinyl acetate, copolymers of vinylpyrrolidoneand of caprolactam, vinyl pyrollidone/vinyl acetate copolymers,copolymers of anionic, cationic and amphoteric monomers, andcombinations thereof.

The water-soluble polymers of the present invention may also be selectedfrom naturally sourced polymers including those of plant origin examplesof which include karaya gum, tragacanth gum, gum Arabic, acemannan,konjac mannan, acacia gum, gum ghatti, whey protein isolate, and soyprotein isolate; seed extracts including guar gum, locust bean gum,quince seed, and psyllium seed; seaweed extracts such as Carrageenan,alginates, and agar; fruit extracts (pectins); those of microbial originincluding xanthan gum, gellan gum, pullulan, hyaluronic acid,chondroitin sulfate, and dextran; and those of animal origin includingcasein, gelatin, keratin, keratin hydrolysates, sulfonic keratins,albumin, collagen, glutelin, glucagons, gluten, zein, and shellac.

Modified natural polymers can also be used as water-soluble polymers inthe present invention. Suitable modified natural polymers include, butare not limited to, cellulose derivatives such ashydroxypropylmethylcellulose, hydroxymethylcellulose,hydroxyethylcellulose, methylcellulose, hydroxypropylcellulose,ethylcellulose, carboxymethylcellulose, cellulose acetate phthalate,nitrocellulose and other cellulose ethers/esters; and guar derivativessuch as hydroxypropyl guar.

The water-soluble polymer of the present invention may include starch.As used herein, the term “starch” include both naturally occurring ormodified starches. Typical natural sources for starches can includecereals, tubers, roots, legumes and fruits. More specific naturalsources can include corn, pea, potato, banana, barley, wheat, rice,sago, amaranth, tapioca, arrowroot, canna, sorghum, and waxy or highamylase varieties thereof. The natural starches can be modified by anymodification method known in the art to form modified starches,including physically modified starches, such as sheared starches orthermally-inhibited starches; chemically modified starches, such asthose which have been cross-linked, acetylated, and organicallyesterified, hydroxyethylated, and hydroxypropylated, phosphorylated, andinorganically esterified, cationic, anionic, nonionic, amphoteric andzwitterionic, and succinate and substituted succinate derivativesthereof; conversion products derived from any of the starches, includingfluidity or thin-boiling starches prepared by oxidation, enzymeconversion, acid hydrolysis, heat or acid dextrinization, thermal and orsheared products may also be useful herein; and pregelatinized starcheswhich are known in the art.

Preferred water-soluble polymers of the present invention includepolyvinyl alcohols, polyvinylpyrrolidones, polyalkylene oxides, starchand starch derivatives, pullulan, gelatin,hydroxypropylmethylcelluloses, methycelluloses, andcarboxymethycelluloses. More preferred water-soluble polymers of thepresent invention include polyvinyl alcohols, andhydroxypropylmethylcelluloses.

Most preferred water-soluble polymers of the present invention arepolyvinyl alcohols characterized by a degree of hydrolysis ranging fromabout 40% to about 100%, preferably from about 50% to about 95%, morepreferably from about 65% to about 92%, most preferably from about 70%to about 90%. Commercially available polyvinyl alcohols include thosefrom Celanese Corporation (Texas, USA) under the CELVOL trade nameincluding, but not limited to, CELVOL 523, CELVOL 530, CELVOL 540,CELVOL 518, CELVOL 513, CELVOL 508, CELVOL 504; those from KurarayEurope GmbH (Frankfurt, Germany) under the Mowiol® and POVAL′ tradenames; and PVA 1788 (also referred to as PVA BP17) commerciallyavailable from various suppliers including Lubon Vinylon Co. (Nanjing,China); and combinations thereof. In a particularly preferred embodimentof the present invention, the flexible, porous, dissolvable solid sheetarticle comprises from about 10% to about 25%, more preferably fromabout 15% to about 23%, by total weight of such article, of a polyvinylalcohol having a weight average molecular weight ranging from 80,000 toabout 150,000 Daltons and a degree of hydrolysis ranging from about 80%to about 90%.

In addition to polyvinyl alcohols as mentioned hereinabove, a singlestarch or a combination of starches may be used as a filler material insuch an amount as to reduce the overall level of water-soluble polymersrequired, so long as it helps provide the solid sheet article with therequisite structure and physical/chemical characteristics as describedherein. However, too much starch may comprise the solubility andstructural integrity of the sheet article. Therefore, in preferredembodiments of the present invention, it is desired that the solid sheetarticle comprises no more than 20%, preferably from 0% to 10%, morepreferably from 0% to 5%, most preferably from 0% to 1%, by weight ofsaid solid sheet article, of starch.

2. Surfactants

In addition to the water-soluble polymer described hereinabove, thesolid sheet article of the present invention comprises one or moresurfactants. The surfactants may function as emulsifying agents duringthe aeration process to create a sufficient amount of stable bubbles forforming the desired OCF structure of the present invention. Further, thesurfactants may function as active ingredients for delivering a desiredcleansing benefit.

In a preferred embodiment of the present invention, the solid sheetarticle comprises one or more surfactants selected from the groupconsisting of anionic surfactants, nonionic surfactants, cationicsurfactants, zwitterionic surfactants, amphoteric surfactants, polymericsurfactants or combinations thereof. Depending on the desiredapplication of such solid sheet article and the desired consumer benefitto be achieved, different surfactants can be selected. One benefit ofthe present invention is that the OCF structures of the solid sheetarticle allow for incorporation of a high surfactant content while stillproviding fast dissolution. Consequently, highly concentrated cleansingcompositions can be formulated into the solid sheet articles of thepresent invention to provide a new and superior cleansing experience tothe consumers.

The surfactant as used herein may include both surfactants from theconventional sense (i.e., those providing a consumer-noticeablelathering effect) and emulsifiers (i.e., those that do not provide anylathering performance but are intended primarily as a process aid inmaking a stable foam structure). Examples of emulsifiers for use as asurfactant component herein include mono- and di-glycerides, fattyalcohols, polyglycerol esters, propylene glycol esters, sorbitan estersand other emulsifiers known or otherwise commonly used to stabilize airinterfaces.

The total amount of surfactants present in the solid sheet article ofthe present invention may range widely from about 5% to about 80%,preferably from about 10% to about 70%, more preferably from about 30%to about 65%, by total weight of said solid sheet article.Correspondingly, the wet pre-mixture may comprise from about 1% to about40% by weight of the wet pre-mixture of surfactant(s), in one embodimentfrom about 2% to about 35% by weight of the wet pre-mixture ofsurfactant(s), in one embodiment from about 5% to about 30% by weight ofthe wet pre-mixture of surfactant(s).

In a preferred embodiment of the present invention, the solid sheetarticle of the present invention is a cleansing product containing fromabout 30% to about 80%, preferably from about 40% to about 70%, morepreferably from about 50% to about 65%, of one or more surfactants bytotal weight of said solid sheet article. In such cases, the wetpre-mixture may comprise from about 10% to about 40% by weight of thewet pre-mixture of surfactant(s), in one embodiment from about 12% toabout 35% by weight of the wet pre-mixture of surfactant(s), in oneembodiment from about 15% to about 30% by weight of the wet pre-mixtureof surfactant(s).

Non-limiting examples of anionic surfactants suitable for use hereininclude alkyl and alkyl ether sulfates, sulfated monoglycerides,sulfonated olefins, alkyl aryl sulfonates, primary or secondary alkanesulfonates, alkyl sulfosuccinates, acyl taurates, acyl isethionates,alkyl glycerylether sulfonate, sulfonated methyl esters, sulfonatedfatty acids, alkyl phosphates, acyl glutamates, acyl sarcosinates, alkylsulfoacetates, acylated peptides, alkyl ether carboxylates, acyllactylates, anionic fluorosurfactants, sodium lauroyl glutamate, andcombinations thereof. One category of anionic surfactants particularlysuitable for practice of the present invention include C₆-C₂₀ linearalkylbenzene sulphonate (LAS) surfactant. LAS surfactants are well knownin the art and can be readily obtained by sulfonating commerciallyavailable linear alkylbenzenes. Exemplary C₁₀-C₂₀ linear alkylbenzenesulfonates that can be used in the present invention include alkalimetal, alkaline earth metal or ammonium salts of C₁₀-C₂₀ linearalkylbenzene sulfonic acids, and preferably the sodium, potassium,magnesium and/or ammonium salts of C₁₁-C₁₈ or C₁₁-C₁₄ linearalkylbenzene sulfonic acids. More preferred are the sodium or potassiumsalts of C₁₂ and/or C₁₄ linear alkylbenzene sulfonic acids, and mostpreferred is the sodium salt of C₁₂ and/or C₁₄ linear alkylbenzenesulfonic acid, i.e., sodium dodecylbenzene sulfonate or sodiumtetradecylbenzene sulfonate.

LAS provides superior cleaning benefit and is especially suitable foruse in laundry detergent applications. It has been a surprising andunexpected discovery of the present invention that when polyvinylalcohol having a higher weight average molecular weight (e.g., fromabout 50,000 to about 400,000 Daltons, preferably from about 60,000 toabout 300,000 Daltons, more preferably from about 70,000 to about200,000 Daltons, most preferably from about 80,000 to about 150,000Daltons) is used as the film-former and carrier, LAS can be used as amajor surfactant, i.e., present in an amount that is more than 50% byweight of the total surfactant content in the solid sheet article,without adversely affecting the film-forming performance and stabilityof the overall composition. Correspondingly, in a particular embodimentof the present invention, LAS is used as the major surfactant in thesolid sheet article. If present, the amount of LAS in the solid sheetarticle of the present invention may range from about 10% to about 70%,preferably from about 20% to about 65%, more preferably from about 40%to about 60%, by total weight of the solid sheet article.

Another category of anionic surfactants suitable for practice of thepresent invention include sodium trideceth sulfates (STS) having aweight average degree of alkoxylation ranging from about 0.5 to about 5,preferably from about 0.8 to about 4, more preferably from about 1 toabout 3, most preferably from about 1.5 to about 2.5. Trideceth is a13-carbon branched alkoxylated hydrocarbon comprising, in oneembodiment, an average of at least 1 methyl branch per molecule. STSused by the present invention may be include ST(EOxPOy)S, while EOxrefers to repeating ethylene oxide units with a repeating number xranging from 0 to 5, preferably from 1 to 4, more preferably from 1 to3, and while POy refers to repeating propylene oxide units with arepeating number y ranging from 0 to 5, preferably from 0 to 4, morepreferably from 0 to 2. It is understood that a material such as ST2Swith a weight average degree of ethoxylation of about 2, for example,may comprise a significant amount of molecules which have no ethoxylate,1 mole ethoxylate, 3 mole ethoxylate, and so on, while the distributionof ethoxylation can be broad, narrow or truncated, which still resultsin an overall weight average degree of ethoxylation of about 2. STS isparticularly suitable for personal cleansing applications, and it hasbeen a surprising and unexpected discovery of the present invention thatwhen polyvinyl alcohol having a higher weight average molecular weight(e.g., from about 50,000 to about 400,000 Daltons, preferably from about60,000 to about 300,000 Daltons, more preferably from about 70,000 toabout 200,000 Daltons, most preferably from about 80,000 to about150,000 Daltons) is used as the film-former and carrier, STS can be usedas a major surfactant, i.e., present in an amount that is more than 50%by weight of the total surfactant content in the solid sheet article,without adversely affecting the film-forming performance and stabilityof the overall composition. Correspondingly, in a particular embodimentof the present invention, STS is used as the major surfactant in thesolid sheet article. If present, the amount of STS in the solid sheetarticle of the present invention may range from about 10% to about 70%,preferably from about 20% to about 65%, more preferably from about 40%to about 60%, by total weight of the solid sheet article.

Another category of anionic surfactants suitable for practice of thepresent invention include alkyl sulfates. These materials have therespective formulae ROSO₃M, wherein R is alkyl or alkenyl of from about6 to about 20 carbon atoms, x is 1 to 10, and M is a water-solublecation such as ammonium, sodium, potassium and triethanolamine.Preferably, R has from about 6 to about 18, preferably from about 8 toabout 16, more preferably from about 10 to about 14, carbon atoms.Previously, unalkoxylated C₆-C₂₀ linear or branched alkyl sulfates (AS)have been considered the preferred surfactants in dissolvable solidsheet articles, especially as the major surfactant therein, due to itscompatibility with low molecular weight polyvinyl alcohols (e.g., thosewith a weight average molecular weight of no more than 50,000 Daltons)in film-forming performance and storage stability. However, it has beena surprising and unexpected discovery of the present invention that whenpolyvinyl alcohol having a higher weight average molecular weight (e.g.,from about 50,000 to about 400,000 Daltons, preferably from about 60,000to about 300,000 Daltons, more preferably from about 70,000 to about200,000 Daltons, most preferably from about 80,000 to about 150,000Daltons) is used as the film-former and carrier, other surfactants, suchas LAS and/or STS, can be used as the major surfactant in the solidsheet article, without adversely affecting the film-forming performanceand stability of the overall composition. Therefore, in a particularlypreferred embodiment of the present invention, it is desirable toprovide a solid sheet article with no more than about 20%, preferablyfrom 0% to about 10%, more preferably from 0% to about 5%, mostpreferably from 0% to about 1%, by weight of said solid sheet article,of AS.

Another category of anionic surfactants suitable for practice of thepresent invention include C₆-C₂₀ linear or branched alkylalkoxy sulfates(AAS). Among this category, linear or branched alkylethoxy sulfates(AES) having the respective formulae RO(C₂H₄O)_(x)SO₃M are particularlypreferred, wherein R is alkyl or alkenyl of from about 6 to about 20carbon atoms, x is 1 to 10, and M is a water-soluble cation such asammonium, sodium, potassium and triethanolamine. Preferably, R has fromabout 6 to about 18, preferably from about 8 to about 16, morepreferably from about 10 to about 14, carbon atoms. The AES surfactantsare typically made as condensation products of ethylene oxide andmonohydric alcohol's having from about 6 to about 20 carbon atoms.Useful alcohols can be derived from fats, e.g., coconut oil or tallow,or can be synthetic. Lauryl alcohol and straight chain alcohol's derivedfrom coconut oil are preferred herein. Such alcohol's are reacted withabout 1 to about 10, preferably from about 3 to about 5, and especiallyabout 3, molar proportions of ethylene oxide and the resulting mixtureof molecular species having, for example, an average of 3 moles ofethylene oxide per mole of alcohol, is sulfated and neutralized. Highlypreferred AES are those comprising a mixture of individual compounds,said mixture having an average alkyl chain length of from about 10 toabout 16 carbon atoms and an average degree of ethoxylation of fromabout 1 to about 4 moles of ethylene oxide. If present, the the amountof AAS in the solid sheet article of the present invention may rangefrom about 2% to about 40%, preferably from about 5% to about 30%, morepreferably from about 8% to about 12%, by total weight of the solidsheet article.

Other suitable anionic surfactants include water-soluble salts of theorganic, sulfuric acid reaction products of the general formula[R¹—SO₃-M], wherein R¹ is chosen from the group consisting of a straightor branched chain, saturated aliphatic hydrocarbon radical having fromabout 6 to about 20, preferably about 10 to about 18, carbon atoms; andM is a cation. Preferred are alkali metal and ammonium sulfonated C₁₀₋₁₈n-paraffins. Other suitable anionic surfactants include olefinsulfonates having about 12 to about 24 carbon atoms. The α-olefins fromwhich the olefin sulfonates are derived are mono-olefins having about 12to about 24 carbon atoms, preferably about 14 to about 16 carbon atoms.Preferably, they are straight chain olefins.

Another class of anionic surfactants suitable for use in the fabric andhome care compositions is the β-alkyloxy alkane sulfonates. Thesecompounds have the following formula:

where R₁ is a straight chain alkyl group having from about 6 to about 20carbon atoms, R₂ is a lower alkyl group having from about 1 (preferred)to about 3 carbon atoms, and M is a water-soluble cation as hereinbeforedescribed.

Additional examples of suitable anionic surfactants are the reactionproducts of fatty acids esterified with isethionic acid and neutralizedwith sodium hydroxide where, for example, the fatty acids are derivedfrom coconut oil; sodium or potassium salts of fatty acid amides ofmethyl tauride in which the fatty acids, for example, are derived fromcoconut oil. Still other suitable anionic surfactants are thesuccinamates, examples of which include disodium N-octadecylsulfosuccinamate; diammoniumlauryl sulfosuccinamate; tetrasodiumN-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinamate; diamyl ester ofsodium sulfosuccinic acid; dihexyl ester of sodium sulfosuccinic acid;and dioctyl esters of sodium sulfosuccinic acid.

Nonionic surfactants that can be included into the solid sheet articleof the present invention may be any conventional nonionic surfactants,including but not limited to: alkyl alkoxylated alcohols, alkylalkoxylated phenols, alkyl polysaccharides (especially alkyl glucosidesand alkyl polyglucosides), polyhydroxy fatty acid amides, alkoxylatedfatty acid esters, sucrose esters, sorbitan esters and alkoxylatedderivatives of sorbitan esters, amine oxides, and the like. Preferrednonionic surfactants are those of the formula R¹(OC₂H₄)_(n)OH, whereinR¹ is a C₈-C₁₈ alkyl group or alkyl phenyl group, and n is from about 1to about 80. Particularly preferred are C₈-C₁₈ alkyl ethoxylatedalcohols having a weight average degree of ethoxylation from about 1 toabout 20, preferably from about 5 to about 15, more preferably fromabout 7 to about 10, such as NEODOL® nonionic surfactants commerciallyavailable from Shell. Other non-limiting examples of nonionicsurfactants useful herein include: C₆-C₁₂ alkyl phenol alkoxylates wherethe alkoxylate units may be ethyleneoxy units, propyleneoxy units, or amixture thereof; C₁₂-C₁₈ alcohol and C₆-C₁₂ alkyl phenol condensateswith ethylene oxide/propylene oxide block polymers such as Pluronic®from BASF; C₁₄-C₂₂ mid-chain branched alcohols (BA); C₁₄-C₂₂ mid-chainbranched alkyl alkoxylates, BAE_(x), wherein x is from 1 to 30; alkylpolysaccharides, specifically alkyl polyglycosides; Polyhydroxy fattyacid amides; and ether capped poly(oxyalkylated) alcohol surfactants.Suitable nonionic surfactants also include those sold under thetradename Lutensol® from BASF.

In a preferred embodiment, the nonionic surfactant is selected fromsorbitan esters and alkoxylated derivatives of sorbitan esters includingsorbitan monolaurate (SPAN® 20), sorbitan monopalmitate (SPAN® 40),sorbitan monostearate (SPAN® 60), sorbitan tristearate (SPAN® 65),sorbitan monooleate (SPAN® 80), sorbitan trioleate (SPAN® 85), sorbitanisostearate, polyoxyethylene (20) sorbitan monolaurate (Tween® 20),polyoxyethylene (20) sorbitan monopalmitate (Tween® 40), polyoxyethylene(20) sorbitan monostearate (Tween® 60), polyoxyethylene (20) sorbitanmonooleate (Tween® 80), polyoxyethylene (4) sorbitan monolaurate (Tween®21), polyoxyethylene (4) sorbitan monostearate (Tween® 61),polyoxyethylene (5) sorbitan monooleate (Tween® 81), all available fromUniqema, and combinations thereof.

The most preferred nonionic surfactants for practice of the presentinvention include C₆-C₂₀ linear or branched alkylalkoxylated alcohols(AA) having a weight average degree of alkoxylation ranging from 5 to15, more preferably C₁₂-C₁₄ linear ethoxylated alcohols having a weightaverage degree of alkoxylation ranging from 7 to 9. If present, theamount of AA-type nonionic surfactant(s) in the solid sheet article ofthe present invention may range from about 2% to about 40%, preferablyfrom about 5% to about 30%, more preferably from about 8% to about 12%,by total weight of the solid sheet article.

Amphoteric surfactants suitable for use in the solid sheet article ofthe present invention includes those that are broadly described asderivatives of aliphatic secondary and tertiary amines in which thealiphatic radical can be straight or branched chain and wherein one ofthe aliphatic substituents contains from about 8 to about 18 carbonatoms and one contains an anionic water solubilizing group, e.g.,carboxy, sulfonate, sulfate, phosphate, or phosphonate. Examples ofcompounds falling within this definition are sodium3-dodecyl-aminopropionate, sodium 3-dodecylaminopropane sulfonate,sodium lauryl sarcosinate, N-alkyltaurines such as the one prepared byreacting dodecylamine with sodium isethionate, and N-higher alkylaspartic acids.

One category of amphoteric surfactants particularly suitable forincorporation into solid sheet articles with personal care applications(e.g., shampoo, facial or body cleanser, and the like) includealkylamphoacetates, such as lauroamphoacetate and cocoamphoacetate.Alkylamphoacetates can be comprised of monoacetates and diacetates. Insome types of alkylamphoacetates, diacetates are impurities orunintended reaction products. If present, the amount ofalkylamphoacetate(s) in the solid sheet article of the present inventionmay range from about 2% to about 40%, preferably from about 5% to about30%, more preferably from about 10% to about 20%, by total weight of thesolid sheet article.

Zwitterionic surfactants suitable include those that are broadlydescribed as derivatives of aliphatic quaternary ammonium, phosphonium,and sulfonium compounds, in which the aliphatic radicals can be straightor branched chain, and wherein one of the aliphatic substituentscontains from about 8 to about 18 carbon atoms and one contains ananionic group, e.g., carboxy, sulfonate, sulfate, phosphate, orphosphonate. Such suitable zwitterionic surfactants can be representedby the formula:

wherein R² contains an alkyl, alkenyl, or hydroxy alkyl radical of fromabout 8 to about 18 carbon atoms, from 0 to about 10 ethylene oxidemoieties and from 0 to about 1 glyceryl moiety; Y is selected from thegroup consisting of nitrogen, phosphorus, and sulfur atoms; R³ is analkyl or monohydroxyalkyl group containing about 1 to about 3 carbonatoms; X is 1 when Y is a sulfur atom, and 2 when Y is a nitrogen orphosphorus atom; R⁴ is an alkylene or hydroxyalkylene of from about 1 toabout 4 carbon atoms and Z is a radical selected from the groupconsisting of carboxylate, sulfonate, sulfate, phosphonate, andphosphate groups.

Other zwitterionic surfactants suitable for use herein include betaines,including high alkyl betaines such as coco dimethyl carboxymethylbetaine, cocoamidopropyl betaine, cocobetaine, lauryl amidopropylbetaine, oleyl betaine, lauryl dimethyl carboxymethyl betaine, lauryldimethyl alphacarboxyethyl betaine, cetyl dimethyl carboxymethylbetaine, lauryl bis-(2-hydroxyethyl) carboxymethyl betaine, stearylbis-(2-hydroxypropyl) carboxymethyl betaine, oleyl dimethylgamma-carboxypropyl betaine, and laurylbis-(2-hydroxypropyl)alpha-carboxyethyl betaine. The sulfobetaines maybe represented by coco dimethyl sulfopropyl betaine, stearyl dimethylsulfopropyl betaine, lauryl dimethyl sulfoethyl betaine, laurylbis-(2-hydroxyethyl) sulfopropyl betaine and the like; amidobetaines andamidosulfobetaines, wherein the RCONH(CH₂)₃ radical, wherein R is aC₁₁-C₁₇ alkyl, is attached to the nitrogen atom of the betaine are alsouseful in this invention.

Cationic surfactants can also be utilized in the present invention,especially in fabric softener and hair conditioner products. When usedin making products that contain cationic surfactants as the majorsurfactants, it is preferred that such cationic surfactants are presentin an amount ranging from about 2% to about 30%, preferably from about3% to about 20%, more preferably from about 5% to about 15% by totalweight of the solid sheet article.

Cationic surfactants may include DEQA compounds, which encompass adescription of diamido actives as well as actives with mixed amido andester linkages. Preferred DEQA compounds are typically made by reactingalkanolamines such as MDEA (methyldiethanolamine) and TEA(triethanolamine) with fatty acids. Some materials that typically resultfrom such reactions include N,N-di(acyl-oxyethyl)-N,N-dimethylammoniumchloride or N,N-di(acyl-oxyethyl)-N,N-methylhydroxyethylammoniummethylsulfate wherein the acyl group is derived from animal fats,unsaturated, and polyunsaturated, fatty acids.

Other suitable actives for use as a cationic surfactant include reactionproducts of fatty acids with dialkylenetriamines in, e.g., a molecularratio of about 2:1, said reaction products containing compounds of theformula:

R¹—C(O)—NH—R²—NH—R³—NH—C(O)—R¹

wherein R¹, R² are defined as above, and each R³ is a C₁₋₆ alkylenegroup, preferably an ethylene group. Examples of these actives arereaction products of tallow acid, canola acid, or oleic acids withdiethylenetriamine in a molecular ratio of about 2:1, said reactionproduct mixture containing N,N″-ditallowoyldiethylenetriamine,N,N″-dicanola-oyldiethylenetriamine, or N,N″-dioleoyldiethylenetriamine,respectively, with the formula:

R¹—C(O)—NH—CH₂CH₂—NH—CH₂CH₂—NH—C(O)—R¹

wherein R² and R³ are divalent ethylene groups, R¹ is defined above andan acceptable examples of this structure when R¹ is the oleoyl group ofa commercially available oleic acid derived from a vegetable or animalsource, include EMERSOL® 223LL or EMERSOL® 7021, available from HenkelCorporation.

Another active for use as a cationic surfactant has the formula:

[R₁—C(O)—NR—R²—N(R)₂—R³—NR—C(O)—R¹]⁺X⁻

wherein R, R¹, R², R³ and X⁻ are defined as above. Examples of thisactive are the di-fatty amidoamines based softener having the formula:

[R¹—C(O)—NH—CH₂CH₂—N(CH₃)(CH₂CH₂OH)—CH₂CH₂—NH—C(O)—R¹]⁺CH₃SO₄ ⁻

wherein R¹—C(O) is an oleoyl group, soft tallow group, or a hardenedtallow group available commercially from Degussa under the trade namesVARISOFT® 222LT, VARISOFT® 222, and VARISOFT® 110, respectively.

A second type of DEQA (“DEQA (2)”) compound suitable as a active for useas a cationic surfactant has the general formula:

[R₃N⁺CH₂CH(YR¹)(CH₂YR¹)]X⁻

wherein each Y, R, R¹, and X⁻ have the same meanings as before. Anexample of a preferred DEQA (2) is the “propyl” ester quaternaryammonium fabric softener active having the formula1,2-di(acyloxy)-3-trimethylammoniopropane chloride.

Suitable polymeric surfactants for use in the personal care compositionsof the present invention include, but are not limited to, blockcopolymers of ethylene oxide and fatty alkyl residues, block copolymersof ethylene oxide and propylene oxide, hydrophobically modifiedpolyacrylates, hydrophobically modified celluloses, silicone polyethers,silicone copolyol esters, diquaternary polydimethylsiloxanes, andco-modified amino/polyether silicones.

3. Plasticizers

In a preferred embodiment of the present invention, the flexible,porous, dissolvable solid sheet article of the present invention furthercomprises a plasticizer, preferably in the amount ranging from about0.1% to about 25%, preferably from about 0.5% to about 20%, morepreferably from about 1% to about 15%, most preferably from 2% to 12%,by total weight of said solid sheet article. Correspondingly, the wetpre-mixture used for forming such solid sheet article may comprise fromabout 0.02% to about 20% by weight of said wet pre-mixture, in oneembodiment from about 0.1% to about 10% by weight of said wetpre-mixture, in one embodiment from about 0.5% to about 5% by weight ofthe wet pre-mixture.

Suitable plasticizers for use in the present invention include, forexample, polyols, copolyols, polycarboxylic acids, polyesters,dimethicone copolyols, and the like.

Examples of useful polyols include, but are not limited to: glycerin,diglycerin, ethylene glycol, polyethylene glycol (especially 200-600),propylene glycol, butylene glycol, pentylene glycol, glycerolderivatives (such as propoxylated glycerol), glycidol, cyclohexanedimethanol, hexanediol, 2,2,4-trimethylpentane-1,3-diol,pentaerythritol, urea, sugar alcohols (such as sorbitol, mannitol,lactitol, xylitol, maltitol, and other mono- and polyhydric alcohols),mono-, di- and oligo-saccharides (such as fructose, glucose, sucrose,maltose, lactose, high fructose corn syrup solids, and dextrins),ascorbic acid, sorbates, ethylene bisformamide, amino acids, and thelike.

Examples of polycarboxylic acids include, but are not limited to citricacid, maleic acid, succinic acid, polyacrylic acid, and polymaleic acid.

Examples of suitable polyesters include, but are not limited to,glycerol triacetate, acetylated-monoglyceride, diethyl phthalate,triethyl citrate, tributyl citrate, acetyl triethyl citrate, acetyltributyl citrate.

Examples of suitable dimethicone copolyols include, but are not limitedto, PEG-12 dimethicone, PEG/PPG-18/18 dimethicone, and PPG-12dimethicone.

Other suitable platicizers include, but are not limited to, alkyl andallyl phthalates; napthalates; lactates (e.g., sodium, ammonium andpotassium salts); sorbeth-30; urea; lactic acid; sodium pyrrolidonecarboxylic acid (PCA); sodium hyraluronate or hyaluronic acid; solublecollagen; modified protein; monosodium L-glutamate; alpha & betahydroxyl acids such as glycolic acid, lactic acid, citric acid, maleicacid and salicylic acid; glyceryl polymethacrylate; polymericplasticizers such as polyquaterniums; proteins and amino acids such asglutamic acid, aspartic acid, and lysine; hydrogen starch hydrolysates;other low molecular weight esters (e.g., esters of C₂-C₁₀ alcohols andacids); and any other water soluble plasticizer known to one skilled inthe art of the foods and plastics industries; and mixtures thereof.

Particularly preferred examples of plasticizers include glycerin,ethylene glycol, polyethylene glycol, propylene glycol, and mixturesthereof. Most preferred plasticizer is glycerin.

4. Additional Ingredients

In addition to the above-described ingredients, e.g., the water-solublepolymer, the surfactant(s) and the plasticizer, the solid sheet articleof the present invention may comprise one or more additionalingredients, depending on its intended application. Such one or moreadditional ingredients may be selected from the group consisting offabric care actives, dishwashing actives, hard surface cleaning actives,beauty and/or skin care actives, personal cleansing actives, hair careactives, oral care actives, feminine care actives, baby care actives,and any combinations thereof.

Suitable fabric care actives include but are not limited to: organicsolvents (linear or branched lower C₁-C₈ alcohols, diols, glycerols orglycols; lower amine solvents such as C₁-C₄ alkanolamines, and mixturesthereof; more specifically 1,2-propanediol, ethanol, glycerol,monoethanolamine and triethanolamine), carriers, hydrotropes, builders,chelants, dispersants, enzymes and enzyme stabilizers, catalyticmaterials, bleaches (including photobleaches) and bleach activators,perfumes (including encapsulated perfumes or perfume microcapsules),colorants (such as pigments and dyes, including hueing dyes),brighteners, dye transfer inhibiting agents, clay soilremoval/anti-redeposition agents, structurants, rheology modifiers, sudssuppressors, processing aids, fabric softeners, anti-microbial agents,and the like.

Suitable hair care actives include but are not limited to: moisturecontrol materials of class II for frizz reduction (salicylic acids andderivatives, organic alcohols, and esters), cationic surfactants(especially the water-insoluble type having a solubility in water at 25°C. of preferably below 0.5 g/100 g of water, more preferably below 0.3g/100 g of water), high melting point fatty compounds (e.g., fattyalcohols, fatty acids, and mixtures thereof with a melting point of 25°C. or higher, preferably 40° C. or higher, more preferably 45° C. orhigher, still more preferably 50° C. or higher), silicone compounds,conditioning agents (such as hydrolyzed collagen with tradename Peptein2000 available from Hormel, vitamin E with tradename Emix-d availablefrom Eisai, panthenol available from Roche, panthenyl ethyl etheravailable from Roche, hydrolyzed keratin, proteins, plant extracts, andnutrients), preservatives (such as benzyl alcohol, methyl paraben,propyl paraben and imidazolidinyl urea), pH adjusting agents (such ascitric acid, sodium citrate, succinic acid, phosphoric acid, sodiumhydroxide, sodium carbonate), salts (such as potassium acetate andsodium chloride), coloring agents, perfumes or fragrances, sequesteringagents (such as disodium ethylenediamine tetra-acetate), ultraviolet andinfrared screening and absorbing agents (such as octyl salicylate), hairbleaching agents, hair perming agents, hair fixatives, anti-dandruffagents, anti-microbial agents, hair growth or restorer agents,co-solvents or other additional solvents, and the like.

Suitable beauty and/or skin care actives include those materialsapproved for use in cosmetics and that are described in reference bookssuch as the CTFA Cosmetic Ingredient Handbook, Second Edition, TheCosmetic, Toiletries, and Fragrance Association, Inc. 1988, 1992.Further non-limiting examples of suitable beauty and/or skin careactives include preservatives, perfumes or fragrances, coloring agentsor dyes, thickeners, moisturizers, emollients, pharmaceutical actives,vitamins or nutrients, sunscreens, deodorants, sensates, plant extracts,nutrients, astringents, cosmetic particles, absorbent particles, fibers,anti-inflammatory agents, skin lightening agents, skin tone agent (whichfunctions to improve the overall skin tone, and may include vitamin B3compounds, sugar amines, hexamidine compounds, salicylic acid,1,3-dihydroxy-4-alkybenzene such as hexylresorcinol and retinoids), skintanning agents, exfoliating agents, humectants, enzymes, antioxidants,free radical scavengers, anti-wrinkle actives, anti-acne agents, acids,bases, minerals, suspending agents, pH modifiers, pigment particles,anti-microbial agents, insect repellents, shaving lotion agents,co-solvents or other additional solvents, and the like.

The solid sheet article of the present invention may further compriseother optional ingredients that are known for use or otherwise useful incompositions, provided that such optional materials are compatible withthe selected essential materials described herein, or do not otherwiseunduly impair product performance.

Non-limiting examples of product type embodiments that can be formed bythe solid sheet article of the present invention include laundrydetergent products, fabric softening products, hand cleansing products,hair shampoo or other hair treatment products, body cleansing products,shaving preparation products, dish cleaning products, personal caresubstrates containing pharmaceutical or other skin care actives,moisturizing products, sunscreen products, beauty or skin care products,deodorizing products, oral care products, feminine cleansing products,baby care products, fragrance-containing products, and so forth.

VI. Conversion of Multiple Sheets into Multilayer Structures

Once the flexible, dissolvable, porous solid sheet articles of thepresent invention is formed, as described hereinabove, two or more ofsuch sheets can be further combined and/or treated to form dissolvablesolid articles of any desirable three-dimensional shapes, including butnot limited to: spherical, cubic, rectangular, oblong, cylindrical, rod,sheet, flower-shaped, fan-shaped, star-shaped, disc-shaped, and thelike. The sheets can be combined and/or treated by any means known inthe art, examples of which include but are not limited to, chemicalmeans, mechanical means, and combinations thereof. Such combinationand/or treatment steps are hereby collectively referred to as a“conversion” process, i.e., which functions to convert two or moreflexible, dissolvable, porous sheets of the present invention into adissolvable solid article with a desired three-dimensional shape.

Conventional dissolvable solid articles have relatively highlength/width-to-thickness ratios, i.e., they are relatively thin, inorder to ensure fast dissolution of such articles in water. Therefore,such dissolvable solid articles typically are typically provided in formof relatively large but thin sheet products, which may be difficult tohandle (e.g., too floppy and easily sticking together and hard toseparate upon use) and are not aesthetically pleasing to the consumers.However, there is little or no space for change or improvement of suchproduct form, due to constraints imparted by the dissolutionrequirement.

It has been a surprising and unexpected discovery of the presentinvention that three-dimensional multilayer solid articles formed bystacking multiple layers of the solid sheet articles of the presentinvention together are more dissolvable than single-layer solid articlesthat have the same aspect ratio. This allows significant extension ofsuch solid articles along the thickness direction, to createthree-dimensional product shapes that are easier to handle and moreaesthetically pleasing to the consumers (e.g., products in form of thickpads or even cubes).

Specifically, the multilayer dissolvable solid articles formed bystacking multiple layers of the solid sheet articles of the presentinvention together is characterized by a maximum dimension D and aminimum dimension z (which is perpendicular to the maximum dimension),while the ratio of D/z (hereinafter also referred to as the “AspectRatio”) ranges from 1 to about 10, preferably from about 1.4 to about 9,preferably from about 1.5 to about 8, more preferably from about 2 toabout 7. Note that when the Aspect Ratio is 1, the dissolvable solidarticle has a spherical shape. When the Aspect Ratio is about 1.4, thedissolvable solid article has a cubical shape.

The multilayer dissolvable solid article of the present invention mayhave a minimal dimension z that is greater than about 3 mm but less thanabout 20 cm, preferably from about 4 mm to about 10 cm, more preferablyfrom about 5 mm to about 30 mm.

The above-described multilayer dissolvable solid article may comprisemore than two of such flexible, dissolvable, porous sheets. For example,it may comprise from about 4 to about 50, preferably from about 5 toabout 40, more preferably from about 6 to about 30, of said flexible,dissolvable, porous sheets. The improved OCF structures in the flexible,dissolvable, porous sheets made according to the present invention allowstacking of many sheets (e.g., 15-40) together, while still providing asatisfactory overall dissolution rate for the stack.

In a particularly preferred embodiment of the present invention, themultilayer dissolvable solid article comprises from 15 to 40 layers ofthe above-described flexible, dissolvable, porous sheets and has anaspect ratio ranging from about 2 to about 7.

The multilayer dissolvable solid article of the present invention maycomprise individual sheets of different colors, which are visual from anexternal surface (e.g., one or more side surfaces) of such article. Suchvisible sheets of different colors are aesthetically pleasing to theconsumers. Further, the different colors of individual sheets mayprovide visual cues indicative of different benefit agents contained inthe individual sheets. For example, the multilayer dissolvable solidarticle may comprise a first sheet that has a first color and contains afirst benefit agent and a second sheet that has a second color andcontains a second benefit, while the first color provides a visual cueindicative of the first benefit agent, and while the second colorprovides a visual cue indicative of the second benefit agent.

Further, one or more functional ingredients can be “sandwiched” betweenindividual sheets of the multilayer dissolvable solid article asdescribed hereinabove, e.g., by spraying, sprinkling, dusting, coating,spreading, dipping, injecting, or even vapor deposition. In order toavoid interference of such functional ingredients with the cutting sealor edge seal near the peripherals of the individual sheets, it ispreferred that such functional ingredients are located within a centralregion between two adjacent sheets, which is defined as a region that isspaced apart from the peripherals of such adjacent sheets by a distancethat is at least 10% of the maximum Dimension D.

Suitable functional ingredients can be selected from the groupconsisting of cleaning actives (surfactants, free perfumes, encapsulatedperfumes, perfume microcapsules, silicones, softening agents, enzymes,bleaches, colorants, builders, rheology modifiers, pH modifiers, andcombinations thereof) and personal care actives (e.g., emollients,humectants, conditioning agents, and combinations thereof).

Test Methods Test 1: Scanning Electron Microscopic (SEM) Method forDetermining Surface Average Pore Diameter of the Sheet Article

A Hitachi TM3000 Tabletop Microscope (S/N: 123104-04) is used to acquireSEM micrographs of samples. Samples of the solid sheet articles of thepresent invention are approximately 1 cm×1 cm in area and cut fromlarger sheets. Images are collected at a magnification of 50×, and theunit is operated at 15 kV. A minimum of 5 micrograph images arecollected from randomly chosen locations across each sample, resultingin a total analyzed area of approximately 43.0 mm² across which theaverage pore diameter is estimated.

The SEM micrographs are then firstly processed using the image analysistoolbox in Matlab. Where required, the images are converted tograyscale. For a given image, a histogram of the intensity values ofevery single pixel is generated using the ‘imhist’ Matlab function.Typically, from such a histogram, two separate distributions areobvious, corresponding to pixels of the brighter sheet surface andpixels of the darker regions within the pores. A threshold value ischosen, corresponding to an intensity value between the peak value ofthese two distributions. All pixels having an intensity value lower thanthis threshold value are then set to an intensity value of 0, whilepixels having an intensity value higher are set to 1, thus producing abinary black and white image. The binary image is then analyzed usingImageJ (https://imagej.nih.gov, version 1.52a), to examine both the porearea fraction and pore size distribution. The scale bar of each image isused to provide a pixel/mm scaling factor. For the analysis, theautomatic thresholding and the analyze particles functions are used toisolate each pore. Output from the analyze function includes the areafraction for the overall image and the pore area and pore perimeter foreach individual pore detected.

Average Pore Diameter is defined as DA50:50% of the total pore area iscomprised of pores having equal or smaller hydraulic diameters than theDA50 average diameter.

Hydraulic diameter=‘4*Pore area (m²)/Pore perimeter (m)’.

It is an equivalent diameter calculated to account for the pores not allbeing circular.

Test 2: Micro-Computed Tomographic (μCT) Method for Determining Overallor Regional Average Pore Size and Average Cell Wall Thickness of theOpen Cell Foams (OCF)

Porosity is the ratio between void-space to the total space occupied bythe OCF. Porosity can be calculated from μCT scans by segmenting thevoid space via thresholding and determining the ratio of void voxels tototal voxels. Similarly, solid volume fraction (SVF) is the ratiobetween solid-space to the total space, and SVF can be calculated as theratio of occupied voxels to total voxels. Both Porosity and SVF areaverage scalar-values that do not provide structural information, suchas, pore size distribution in the height-direction of the OCF, or theaverage cell wall thickness of OCF struts.

To characterize the 3D structure of the OCFs, samples are imaged using aμCT X-ray scanning instrument capable of acquiring a dataset at highisotropic spatial resolution. One example of suitable instrumentation isthe SCANCO system model 50 μCT scanner (Scanco Medical AG, Bruttisellen,Switzerland) operated with the following settings: energy level of 45kVp at 133 μA; 3000 projections; 15 mm field of view; 750 ms integrationtime; an averaging of 5; and a voxel size of 3 μm per pixel. Afterscanning and subsequent data reconstruction is complete, the scannersystem creates a 16 bit data set, referred to as an ISQ file, where greylevels reflect changes in x-ray attenuation, which in turn relates tomaterial density. The ISQ file is then converted to 8 bit using ascaling factor.

Scanned OCF samples are normally prepared by punching a core ofapproximately 14 mm in diameter. The OCF punch is laid flat on alow-attenuating foam and then mounted in a 15 mm diameter plasticcylindrical tube for scanning. Scans of the samples are acquired suchthat the entire volume of all the mounted cut sample is included in thedataset. From this larger dataset, a smaller sub-volume of the sampledataset is extracted from the total cross section of the scanned OCF,creating a 3D slab of data, where pores can be qualitatively assessedwithout edge/boundary effects.

To characterize pore-size distribution in the height-direction, and thestrut-size, Local Thickness Map algorithm, or LTM, is implemented on thesubvolume dataset. The LTM Method starts with a Euclidean DistanceMapping (EDM) which assigns grey level values equal to the distance eachvoid voxel is from its nearest boundary. Based on the EDM data, the 3Dvoid space representing pores (or the 3D solid space representingstruts) is tessellated with spheres sized to match the EDM values.Voxels enclosed by the spheres are assigned the radius value of thelargest sphere. In other words, each void voxel (or solid voxel forstruts) is assigned the radial value of the largest sphere that thatboth fits within the void space boundary (or solid space boundary forstruts) and includes the assigned voxel.

The 3D labelled sphere distribution output from the LTM data scan can betreated as a stack of two dimensional images in the height-direction (orZ-direction) and used to estimate the change in sphere diameter fromslice to slice as a function of OCF depth. The strut thickness istreated as a 3D dataset and an average value can be assessed for thewhole or parts of the subvolume. The calculations and measurements weredone using AVIZO Lite (9.2.0) from Thermo Fisher Scientific and MATLAB(R2017a) from Mathworks.

Test 3: Percent Open Cell Content of the Sheet Article

The Percent Open Cell Content is measured via gas pycnometry. Gaspycnometry is a common analytical technique that uses a gas displacementmethod to measure volume accurately. Inert gases, such as helium ornitrogen, are used as the displacement medium. A sample of the solidsheet article of the present invention is sealed in the instrumentcompartment of known volume, the appropriate inert gas is admitted, andthen expanded into another precision internal volume. The pressurebefore and after expansion is measured and used to compute the samplearticle volume.

ASTM Standard Test Method D2856 provides a procedure for determining thepercentage of open cells using an older model of an air comparisonpycnometer. This device is no longer manufactured. However, one candetermine the percentage of open cells conveniently and with precisionby performing a test which uses Micromeritics' AccuPyc Pycnometer. TheASTM procedure D2856 describes 5 methods (A, B, C, D, and E) fordetermining the percent of open cells of foam materials. For theseexperiments, the samples can be analyzed using an Accupyc 1340 usingnitrogen gas with the ASTM foampyc software. Method C of the ASTMprocedure is to be used to calculate to percent open cells. This methodsimply compares the geometric volume as determined using calipers andstandard volume calculations to the open cell volume as measured by theAccupyc, according to the following equation:

Open cell percentage=Open cell volume of sample/Geometric volume ofsample*100

It is recommended that these measurements be conducted by MicromereticsAnalytical Services, Inc. (One Micromeritics Dr, Suite 200, Norcross,Ga. 30093). More information on this technique is available on theMicromeretics Analytical Services web sites (www.particletesting.com orwww.micromeritics.com), or published in “Analytical Methods in Fineparticle Technology” by Clyde Orr and Paul Webb.

Test 4: Final Moisture Content of the Sheet Article

Final moisture content of the solid sheet article of the presentinvention is obtained by using a Mettler Toledo HX204 Moisture Analyzer(S/N B706673091). A minimum of 1 g of the dried sheet article is placedon the measuring tray. The standard program is then executed, withadditional program settings of 10 minutes analysis time and atemperature of 110° C.

Test 5: Thickness of the Sheet Article

Thickness of the flexible, porous, dissolvable solid sheet article ofthe present invention is obtained by using a micrometer or thicknessgage, such as the Mitutoyo Corporation Digital Disk Stand MicrometerModel Number IDS-1012E (Mitutoyo Corporation, 965 Corporate Blvd,Aurora, Ill., USA 60504). The micrometer has a 1-inch diameter platenweighing about 32 grams, which measures thickness at an applicationpressure of about 0.09 psi (6.32 gm/cm²).

The thickness of the flexible, porous, dissolvable solid sheet articleis measured by raising the platen, placing a section of the sheetarticle on the stand beneath the platen, carefully lowering the platento contact the sheet article, releasing the platen, and measuring thethickness of the sheet article in millimeters on the digital readout.The sheet article should be fully extended to all edges of the platen tomake sure thickness is measured at the lowest possible surface pressure,except for the case of more rigid substrates which are not flat.

Test 6: Basis Weight of the Sheet Article

Basis Weight of the flexible, porous, dissolvable solid sheet article ofthe present invention is calculated as the weight of the sheet articleper area thereof (grams/m²). The area is calculated as the projectedarea onto a flat surface perpendicular to the outer edges of the sheetarticle. The solid sheet articles of the present invention are cut intosample squares of 10 cm×10 cm, so the area is known. Each of such samplesquares is then weighed, and the resulting weight is then divided by theknown area of 100 cm² to determine the corresponding basis weight.

For an article of an irregular shape, if it is a flat object, the areais thus computed based on the area enclosed within the outer perimeterof such object. For a spherical object, the area is thus computed basedon the average diameter as 3.14×(diameter/2)². For a cylindrical object,the area is thus computed based on the average diameter and averagelength as diameter x length. For an irregularly shaped three-dimensionalobject, the area is computed based on the side with the largest outerdimensions projected onto a flat surface oriented perpendicularly tothis side. This can be accomplished by carefully tracing the outerdimensions of the object onto a piece of graph paper with a pencil andthen computing the area by approximate counting of the squares andmultiplying by the known area of the squares or by taking a picture ofthe traced area (shaded-in for contrast) including a scale and usingimage analysis techniques.

Test 7: Density of the Sheet Article

Density of the flexible, porous, dissolvable solid sheet article of thepresent invention is determined by the equation: CalculatedDensity=Basis Weight of porous solid/(Porous Solid Thickness×1,000). TheBasis Weight and Thickness of the dissolvable porous solid aredetermined in accordance with the methodologies described hereinabove.

Test 8: Specific Surface Area of the Sheet Article

The Specific Surface Area of the flexible, porous, dissolvable solidsheet article is measured via a gas adsorption technique. Surface Areais a measure of the exposed surface of a solid sample on the molecularscale. The BET (Brunauer, Emmet, and Teller) theory is the most popularmodel used to determine the surface area and is based upon gasadsorption isotherms. Gas Adsorption uses physical adsorption andcapillary condensation to measure a gas adsorption isotherm. Thetechnique is summarized by the following steps; a sample is placed in asample tube and is heated under vacuum or flowing gas to removecontamination on the surface of the sample. The sample weight isobtained by subtracting the empty sample tube weight from the combinedweight of the degassed sample and the sample tube. The sample tube isthen placed on the analysis port and the analysis is started. The firststep in the analysis process is to evacuate the sample tube, followed bya measurement of the free space volume in the sample tube using heliumgas at liquid nitrogen temperatures. The sample is then evacuated asecond time to remove the helium gas. The instrument then beginscollecting the adsorption isotherm by dosing krypton gas at userspecified intervals until the requested pressure measurements areachieved. Samples may then analyzed using an ASAP 2420 with krypton gasadsorption. It is recommended that these measurements be conducted byMicromeretics Analytical Services, Inc. (One Micromeritics Dr, Suite200, Norcross, Ga. 30093). More information on this technique isavailable on the Micromeretics Analytical Services web sites(www.particletesting.com or www.micromeritics.com), or published in abook, “Analytical Methods in Fine Particle Technology”, by Clyde Orr andPaul Webb.

Test 9: Dissolution Rate

Firstly, the solid sheets are stored under ambient relative humidity of50±2% and ambient temperature of 23±1° C. for 24 hours (i.e., aconditioning step). Following the initial conditioning step describedabove, 25 mm diameter discs are firstly cut from the large solid sheetusing a 25 mm hollow hole punch. The required number of foam discs isset such that the total mass of all foam discs is no less than 0.1 g.

The required number of foam discs are then stacked in a head to toeorientation and placed inside an Omnifit™ EZ chromatography column(006EZ-25-10-AF) having 25 mm inner diameter, 100 m length and anadjustable, removable endpiece. The stack of foam discs is placed insidethe column such that the direction of flow through the column isperpendicular to the top surface of the foam discs. Once placed insidethe column, the endpiece is inserted into the column and adjusted untilthe perpendicular distance between the two inner frits is equal to thethickness of the stack of foam discs.

Masterflex silicone tubing (MFLEX SILICONE #25 25′) and a Masterflexperistaltic pump (MFLX L/S 1CH 300R 115/230 13124) are used to controlthe flow of water through the column. The system flow rate is calibratedby flowing water through the pump, tubing and an empty column atdifferent pump RPM settings and recording the volume of water collectedover a defined period of time. For all experiments a flow rate of 5litres per hour was utilized.

The inlet and outlet tubing are both placed inside a 1 litre beakercontaining 500 ml of deionised water at ambient temperature. The beakeris placed on a magnetic stirrer plate, and a magnetic stirrer bar havinglength 23 mm and thickness 10 mm is placed in the beaker, and thestirrer rotation speed is set to 300 rpm. A Mettler Toledo 5230conductivity meter is calibrated to 1413 μS/cm and the probe placed inthe beaker of water.

The flow of water through the system is started. Once the first drops ofwater can be visibly seen inside the column and in contact with thefoam, the data recording function of the conductivity meter is started.Data is recorded for at least 20 minutes.

In order to estimate the time required to reach a 90 or 95% percentagedissolution of the foam, a calibration curve is firstly generated wherelayers of the foam discs are dropped one a time into a stirred beaker of500 ml deionised water. The mass of each individual foam disc, and theconductivity after 5 minutes are both recorded. This process is repeatedfor up to 5 discs total. A linear function is fitted to the data, whichis then used to estimate the maximum conductivity in each dissolutionexperiment based on the total mass of the foam discs placed in thecolumn. The percentage dissolution is then calculated as

% Dissolution=Experimentally measured conductivity/Maximumconductivity*100

The time required to achieve 90 or 95 percentage dissolution is thenfound from this calculated data. The calibration procedure is repeatedfor each formula tested.

Test 10: Bubble Size

The bubble size of aerated pre-mixture is measured as follows:

Rectangular glass cover slides, having a width and a length of 2 cm anda thickness of 1 mm are firstly glued onto a glass slide having a widthof 6 cm and a length of 2 cm, such that a cavity having a thickness of 1mm, a length of 2 cm and a width of slightly less than 2 cm is locatedin the center of the glass slide. The width of the cavity must be keptat less than 2 cm so that an additional cover slide can be placed on topof the cavity.

To capture the image for bubble size analysis, the aerated liquid foamis deposited into the cavity using a spatula and another cover slideplaced on top and pressed down gently, in order to reduce the thicknessof the liquid to 1 mm.

A SMZ-T4 Chongqing Optec microscope and RZIMAGE MicroUL300 digitalcamera were used to capture the images. The glass slide was placed ontothe backlit area of the microscope, and the magnification adjusted suchthat the image area was no less than 16 mm². An additional image wastaken with a transparent ruler placed in the image area, such that thegraduated lines could be seen and used to determine the pixel todistance ratio.

The bubble sizes were calculated using the ‘imfindcircles’ function inthe Image Analysis Toolbox of the Matlab 2017b software. For each image,the function was called four times, for pixel size ranges of 21 to 40,41 to 50, 51 to 100 and 101 to 200, respectively, where 20 pixelscorresponds to an approximate length of 60 micron. The sensitivityparameter was set to 0.95. The bubble radii estimated from each call ofthe function were combined to generate a single distribution, and theradii converted to microns using the calibration image generated withthe transparent ruler.

EXAMPLES Example 1: Different OCF Structures in Solid Sheet ArticlesMade by Different Heating/Drying Arrangements

Wet pre-mixtures with the following surfactant/polymer compositions asdescribed in Table 1 and Table 2 below are prepared, for laundry careand hair care articles, respectively.

TABLE 1 (LAUNDRY CARE FORMULATION) Materials: (Wet) w/w % (Dry) w/w %Polyvinyl alcohol (with a degree of 7.58 21 polymerization of about1700, a hydrolysis level of 88%) Glycerin 1.08 3 Linear AlkylbenzeneSulfonate 19.12 53 Sodium Laureth-3 Sulfate 3.61 10 C12-C14 Ethoxylatedalcohol 3.61 10 Water Balance Balance

Viscosity of the wet pre-mixture composition as described in Table 1 isabout 14309.8 cps. After aeration, the average density of such aeratedwet pre-mixture is about 0.25 g/cm³.

TABLE 2 (HAIR CARE FORMULATION - SHAMPOO) Materials: (Wet) w/w % (Dry)w/w % Polyvinyl alcohol (with a degree of 6.85 23.69 polymerization ofabout 1700, a hydrolysis level of 88%) Glycerin 2.75 9.51 Sodium LaurylSulfate 9.52 32.89 Sodium Laureth-3 Sulfate 3.01 10.42 SodiumLauroamphoacetate 5 17.28 Citric acid (anhydrous) 0.93 3.21 WaterBalance Balance

Viscosity of the wet pre-mixture composition as described in Table 2 isabout 19254.6 cps. After aeration, the average density of such aeratedwet pre-mixture is about 0.225 g/cm³.

Flexible, porous, dissolvable solid sheet articles A and B are preparedfrom the above wet pre-mixtures as described in Tables 1 and 2 using acontinuous aerator (Aeros) and a rotary drum dryer in which a spinningbar is employed to feed the aerated wet pre-mixture onto the drum dryer,with the following settings and conditions as described in Table 3below:

TABLE 3 (DRUM DRYING) Parameters Value Wet pre-mixture temperaturebefore and 80° C. during aeration Aeros feed pump speed setting 600Aeros mixing head speed setting 500 Aeros air flow rate setting 100 Wetpre-mixture temperature before drying 60° C. Spinning bar speed 150 rpmDistance between spinning bar and drum dryer 2 mm Rotary drum dryersurface temperature 130° C. Rotary drum dryer rotational speed 0.160 rpmDrying time 4.52 min

A flexible, porous, dissolvable solid sheet article C is also preparedfrom the above wet pre-mixture as described in Table 2 using acontinuous aerator (Oakes) and a mold placed on a hot plate (whichprovides bottom conduction-based heating), with the following settingsand conditions as described in Table 4 below:

TABLE 4 (HOT PLATE DRYING) Parameters Value Wet pre-mixture temperaturebefore and 80° C. during aeration Oakes air flow meter setting 19.2L/hour Oakes pump meter speed setting 20 rpm Oakes mixing head speed1500 rpm Mold depth 1.0 mm Hot plate surface temperature 130° C. Dryingtime 12.5 min

Further, flexible, porous, dissolvable solid sheet articles I and II areprepared from the above wet pre-mixtures described in Tables 1 and 2using a continuous aerator (Oakes) and a mold placed on an impingementoven, with the following settings and conditions as described in Table 5below:

TABLE 5 (IMPINGEMENT OVEN DRYING) Parameters Value Wet pre-mixturetemperature before and 80° C. during aeration Oakes air flow metersetting 19.2 L/hour Oakes pump meter speed setting 20 rpm Oakes mixinghead speed 1500 rpm Mold depth 1.0 mm Impingement oven temperature 130°C. Drying time 6 min

Tables 6-9 as follows summarize various physical parameters and porestructures measured for the solid sheet articles A-C and solid sheetarticles I-II made from the above-described wet pre-mixtures and dryingprocesses.

TABLE 6 (PHYSICAL PARAMETERS) Average Specific Basis Average AverageSurface Drying Weight Density Thickness Area Samples Formulation Processg/m² g/cm³ mm m²/g A Laundry Care Rotary Drum 147.5 0.118 1.265 0.115 BHair Care Rotary Drum 138.4 0.111 1.254 0.107 C Hair Care Hot Plate216.3 0.111 1.968 — I Laundry Care Impingement 116.83 0.118 1.002 — OvenII Hair Care Impingement 212.9 0.111 1.929 — Oven

TABLE 7 (OVERALL PORE STRUCTURES) Percent Overall Average Open CellAverage Cell Wall Sam- Drying Content Pore Size Thickness plesFormulation Process % μm μm A Laundry Care Rotary Drum 90.75 467.1 54.3B Hair Care Rotary Drum 93.54 466.9 42.8 C Hair Care Hot Plate — 287.419.7 I Laundry Care Impingement — 197.6 15.2 Oven II Hair CareImpingement — 325.1 18.7 Oven

TABLE 8 (SURFACE AND REGIONAL PORE STRUCTURES) Surface Average PoreDiameter Drying (μm) Average Pore Size (μm) Samples Formulation ProcessTop Top Middle Bottom A Laundry Care Rotary Drum 201.5 458.3 479.1 463.9B Hair Care Rotary Drum 138.2 412.4 519.0 469.1 C Hair Care Hot Plate120.8 259.7 292.0 309.9 I Laundry Care Impingement 53.3 139.9 213.1238.7 Oven II Hair Care Impingement 60.0 190.7 362.6 419.6 Oven

TABLE 9 (VARIATIONS BETWEEN REGIONAL PORE STRUCTURES) Btw-Region Ratiosof Cross-Region Average Pore Sizes Drying Relative STD Bottom- Bottom-Middle- Samples Formulation Process (%) to-Top to-Middle to-Top ALaundry Care Rotary Drum 2.31% 1.012 0.968 1.046 B Hair Care Rotary Drum11.43% 1.137 0.904 1.259 C Hair Care Hot Plate 8.84% 1.193 1.061 1.124 ILaundry Care Impingement 25.99% 1.706 1.120 1.523 Oven II Hair CareImpingement 36.74% 2.200 1.157 1.901 Oven

The above data demonstrates that when the heating direction is offsetfrom the gravitation direction during most of the drying step, theresulting solid sheet article (e.g., Articles A, B and C) may have a topsurface with larger pore openings and reduced pore size variations indifferent regions along the direction across the thickness of such sheetarticle compared to the solid sheet articles obtained when the heatingdirection is substantially aligned with the gravitational direction(e.g., Articles I and II). Particularly, the above tables show thatArticles A, B and C have Top Surface Average Pore Diameters of greaterthan 100 μm, while the Articles I and II do not. Specifically, FIG. 6Ashows a Scanning Electron Microscopic (SEM) image of the top surface ofArticle A, while FIG. 6B shows a SEM image of the top surface of ArticleI. FIG. 7A shows a SEM image of the top surface of Article C, while FIG.7B shows a SEM image of the top surface of Article II.

Example 2: Increased Bubble Size in an Aged Aerated Pre-Mixture Comparedto an Aerated Pre-Mixture Before the Aging Step

A wet pre-mixture (i.e., a slurry) containing the ingredients of thesolid sheet article (Formulation 1) shown in the following Table 10 andadditional water is prepared, to result in a total solids content ofabout 35% by weight (i.e., the total water content in the slurry isabout 65% by weight).

TABLE 10 Formulation 1 Materials (Dry), wt % (Fabric Care) Polyvinylalcohol (with a degree of polymerization 18.00 of about 1700, ahydrolysis level of 88%) Polyvinyl alcohol (with a degree ofpolymerization 6.00 of about 500, a hydrolysis level of 88%) Glycerin3.51 Linear Alkylbenzene Sulfonate 40.00 Sodium Laureth-3 Sulfate 4.60C12-C14 Ethoxylated alcohol 16.00 Ethoxylated Polyethyleneimine 1.50Palm kernel fatty acid soap powder 2.07 Sodium Aluminosilicate(crystalline)/Zeolite 0.95 Denatonium Benzoate 0.04 Water 6.00Miscellaneous Q.S.

The method of slurry preparation is as follows:

-   -   1. Water and glycerin are firstly added together into a glass        beaker and stirred at 200 rpm using an overhead stirrer.    -   2. While continuing to stir, the polyvinyl alcohol is then        slowly added into the beaker containing water and glycerin,        ensuring that no foaming of the solution or clumping of the        polyvinyl alcohol occurred.    -   3. The beaker is then placed in a water bath and heated to        80° C. while continuing stirring. The beaker is covered with        clingfilm or tinfoil in order to mitigate water evaporation and        left to continue mixing for at least 1.0 hour.    -   4. The remaining components are weighed and added together in a        separate glass beaker. The balance of water required to achieve        65% total water content in the slurry is also added to this        beaker.    -   5. This beaker is placed in a water bath at 80° C., and its        contents are stirred using an overhead stirrer at 500 rpm for at        least 30 minutes.    -   6. Once the predefined mixing time is reached in both beakers,        the contents of both are added together into a single glass        beaker, followed by continued stirring at 500 rpm and the        temperature is maintained at 80° C. for at least another 30        minutes.

The slurry so formed is then aerated as follows:

-   -   1. An Aeros A20 continuous aerator, consisting of a jacketed        hopper (model JCABT10) and A20 mixing head, is preheated to        80° C. using a water bath and pump.    -   2. The slurry prepared previously is then added to the hopper.        The aerator unit is then switched on and the mixing head speed,        feed pump speed, and air flow rates were set to 600, 500 and 100        respectively.    -   3. The aerated slurry is collected from the aerator outlet and        its density measured by filling a density cup of known volume        and weighing the mass of the aerated slurry. At the aerator        settings described above, an aerated slurry density of about        0.225 g/cm³ is achieved.

Then, the aerated slurry collected from the Aeros A20 outlet is aged for70 minutes in a bucket (open) without any stirring at ambienttemperature. At different time points from 0 min (i.e., the sample istaken immediately after the bucket is filled up with the aerated slurryexited the outlet of the aerator) to 70 min (i.e., after the completionof the aging step), a sample of the aerated slurry is taken out from thebucket. Then, the bubble size of the aerated slurry is determinedaccording to Test 10 and is shown in the following table.

TABLE 11 (BUBBLE SIZE GROWTH OVER AGING TIME) Ageing Average bubble size% of bubbles having average time (μm) diameter greater than 100 μm 0<60*   0 10 84.1  7% 20 86.2 10% 30 84.3  8% 45 94.4 28% 60 95.0 30% 7099.8 41% *A minimum threshold of 60 micron was utilized for the bubbledetection. For the sample analyzed immediately after aeration, nobubbles above 60 micron were detected.

The above table shows that bubbles gradually expand over time during theaging step. Further, FIGS. 8A and 8B respectively show a photo ofbubbles in the slurry of Formulation 1 at 70 min (FIG. 8A) and at 0 min(FIG. 8B) of a 70-min aging step under optical microscopy using the samemagnification. These data indicate that, surprisingly, the bubbles afterthe aging step are much larger than that at the beginning of the agingstep immediately after the aeration. Thus, the introduction of a quitelong aging step (for example, up to 70 minutes) does not result incollapse of bubbles, but significantly increase the bubble size. Theincreased bubble size would result in larger pores in the solid sheetarticle formed by the slurry, and in turn, improved dissolution profileof the solid sheet article.

Example 3: Improved Pore Structure and Improved Dissolution Profile ofthe Solid Sheet Article Achieved by Introduction of an Aging Step in aDrum Dryer Process

1) Preparation of Solid Sheet Articles

Similarly as Example 2, a wet pre-mixture (i.e., a slurry) ofFormulation 1 and additional water is prepared and then aerated toprovide an aerated slurry density of about 0.225 g/cm³.

An inventive, flexible, porous and solid sheet article (Article 1) and acomparative, flexible, porous and solid sheet article (Article 2) areproduced using a rotary drum dryer system comprising a feeding troughand a spinning bar (for example, the system shown in FIG. 5), in whichArticle 1 is prepared in a process having an aging step after theaeration, and Article 2 is prepared in a process in which drying isconducted immediately after the aeration (no aging step).

The method for preparing Articles 1 and 2 from the wet pre-mixtures areas follows:

-   -   1. The rotary drum dryer (having a drum diameter of about 1.5 m)        is pre-heated to about 130° C.    -   2. The aerated slurry collected from the Aeros A20 outlet is        added to the feeding trough of the drum dryer.    -   3. For the inventive sheet article (Article 1), the aerated        slurry is aged in the bucket for a total aging time of 120        minutes. Then, the aged aerated slurry is removed from the        bucket to the feeding trough.    -   4. Articles 1 and 2 are formed by feeding the aerated slurry        onto the surface of the rotating drum dryer with the spinning        bar that is rotating in an opposite direction to the rotating        drum dryer (for example, clockwise vs. counterclockwise) in        which the rotating speed of the drum dryer is set so that the        slurry residence time on the heated drum is about 15 minutes.        For the inventive sheet article (Article 1), the rotating speed        of the spinning bar is relatively low (i.e. 30 rpm) and the        distance between the spinning bar and the surface of the drum        dryer is relatively long (i.e. 8 mm). Under such conditions, the        slurry can be fed onto the surface of the rotating drum dryer        without further introducing air bubbles. For the comparative        sheet article (Article 2), the rotating speed of the spinning        bar is relatively high (i.e. 180 rpm) and the distance between        the spinning bar and the surface of the drum dryer is relatively        short (i.e. 4.5 mm). Under such conditions, the slurry is        vigorously stirred at the air interface and as such, air bubbles        are further introduced into the slurry. As such, the effect        caused by the aging step is reversed or at least compromised by        this additional aeration, which may be considered to be        comparable with a process without an aging step. A leveling        blade that is placed near the slurry pick-up location is        employed to ensure a consistent thickness of the sheet (about        0.8-1.5 mm).    -   5. Once dried, the flexible and porous sheets so formed are        peeled from the drum surface and placed in a plastic bag.

2) Larger Bubble Size in the Slurry Achieved by Introduction of an AgingStep

A sample of the aerated slurry for Article 1 or 2 is respectively takenout from the feeding trough near the feeding location of the slurry.Then, the bubble size of the slurry is determined according to Test 10and is shown in the following table.

TABLE 12 Average bubble size % of bubbles having average Sample (μm)diameter greater than 200 μm Article 1 135.2 8.3% (Inventive) Article 2106.4 1.4% (Comparative)

The above table shows that bubbles in the slurry obtained after an agingstep (Article 1) are much larger than that in the slurry obtainedwithout an aging step (Article 2). Further, FIGS. 9A and 9B respectivelyshow a photo of bubbles in the slurry for Articles 1 and 2 under opticalmicroscopy using the same magnification. These data indicate that, inthe drum drying process, introduction of an aging step after theaeration results in much larger bubbles in the pre-mixture fed onto thedrum dryer. On the contrary, if the aerated pre-mixture is fed onto thedrum dryer immediately after the aeration, the bubbles remain relativelysmall.

3) Improved Pore Structure of Solid Sheet Articles Achieved byIntroduction of an Aging Step

SEM testing is carried out according to Test 1. FIG. 10A and FIG. 10Brespectively show a SEM image of the top surface of Articles 1 and 2,and the following table shows the pore structure for Articles 1 and 2.These data indicate that the inventive sheet article (i.e., Article 1)has significantly larger pores on its top surface and also significantlylarger average pore size compared to the comparative sheet article(i.e., Article 2).

TABLE 13 Top Surface Pore Structure Total Pore Surface Structure AveragePore Average Pore Sample % Pore area Diameter (μm) Diameter (μm) Article1 57.9 427.3 341.2 (Inventive) Article 2 48.7 169.2 223.2 (Comparative)

4) Improved Dissolution Profile of Solid Sheet Articles Achieved byIntroduction of an Aging Step

Dissolution rates for Sheets 1 and 2 are determined according to Test 9.The following Table 14 as well as FIG. 11 shows the results of thedissolution rate testing, indicating the inventive sheet article(Article 1) has a significantly improved dissolution profiles comparedto the comparative sheet article (Article 2). Particularly, the time forthe dissolution of 90% of Article 1 is only 301 seconds, while the timefor the dissolution of 90% of Article 2 is 928 seconds that is more thanthree folds of that for Article 1.

TABLE 14 Article 1 Article 2 % Dissolution Time, seconds Time, secondsRelative % 90% 301 928 208% 95% 479 Not reached —

In conclusion, the introduction of an aging step (i.e., maintaining theaerated pre-mixture for a while after the aeration) in a drum dryerprocess brings about a significantly improved pore structures andthereby a significantly improved dissolution profile.

Example 4: Improved Pore Structure of the Solid Sheet Article Achievedby Introduction of an Aging Step in a Belt Drying Process

1) Preparation of Solid Sheet Articles

Similarly as Example 2, a wet pre-mixture (i.e., a slurry) ofFormulation 2 in the following Table 15 and additional water is preparedand then aerated to provide an aerated slurry density of about 0.225g/cm³.

TABLE 15 Formulation 2 Materials (Dry), wt % (Fabric Care) Polyvinylalcohol (with a degree of polymerization 18.00 of about 1700, ahydrolysis level of 88%) Glycerin 9.00 Linear Alkylbenzene Sulfonate56.00 Sodium Laureth-3 Sulfate 6.00 Ethoxylated Polyethyleneimine 2.00Palm kernel fatty acid soap powder 2.00 Water 7.00 Miscellaneous Q.S.

An inventive, flexible, porous and solid sheet article (Article 3) and acomparative, flexible, porous and solid sheet article (Article 4) areproduced using a belt drying system instead of the drum drying process.In the belt drying system, the drying surface is a movingstainless-steel belt of approximately 4 m length and 60 cm width whichis heated from underneath by hot air convection. The aerated slurry ispumped from the continuous aerator to a 50 litre stainless steel heatedvessel, where it was stored for varying amounts of time (i.e., agingtime) to allow the bubble size to increase. To feed the slurry onto thedrying surface of the moving belt, the vessel was placed above thedrying surface and an outlet positioned at the bottom of the vessel wasopened to allow a steady flow of the slurry onto the belt surface. Athickness control blade was positioned near this depositing location inorder to accumulate excess slurry, and only carry a defined volume (i.e.thickness) of slurry along the drying surface for drying and subsequentremoval. Once dried, the flexible and porous sheets so formed are peeledfrom the drum surface and placed in a plastic bag. The settings of thebelt dryer process are shown in the following table.

TABLE 16 (BELT DRYER PROCESS SETTINGS) Settings Article 3 Article 4Average belt temperature (° C.) 130 130 Belt speed (m/min) 0.6 0.6 Agingtime (min) 15 0

2) Improved Pore Structure of Solid Sheet Articles Achieved byIntroduction of an Aging Step

SEM testing is carried out according to Test 1 for Sheets 3 and 4. FIG.12A and FIG. 12B respectively show a SEM image of the top surface ofSheets 3 and 4, and the following table shows the pore structure forSheets 3 and 4 as determined according to Test 1. These data indicatethat inventive sheet articles (i.e., Article 3) has significantly largerpores on its top surface and also significantly larger average pore sizecompared to comparative sheet articles (i.e., Article 4).

TABLE 17 Top Surface Pore Structure Total Pore Surface Structure AveragePore Average Pore Sample % Pore area Diameter (μm) Diameter (μm) Article3 62.1 402.1 366.1 (Inventive) Article 4 30.6 169.2 225.4 (Comparative)

In conclusion, the introduction of an aging step (i.e., maintaining theaerated pre-mixture for a while after the aeration) in a belt dryerprocess also brings about a significantly improved pore structure.

Example 5: Improved Pore Structure and Improved Dissolution Profile ofthe Solid Sheet Article Achieved by Introduction of an Aging Step in aDrum Dryer Process Involving a Feeding Die

1) Preparation of Solid Sheet Articles

Similarly as Example 2, a wet pre-mixture (i.e., a slurry) ofFormulation 3 in the following Table 18 and additional water is preparedand then aerated to provide an aerated slurry density of about 0.225g/cm³.

TABLE 18 Formulation 3 Materials (Dry), wt % (Personal Care) Polyvinylalcohol (with a degree of polymerization 28.10 of about 1700, ahydrolysis of 88%) Glycerin 9.60 Sodium Lauroamphoacetate 11.30 SodiumLauramidopropyl Betaine 28.10 Sodium Lauroyl Methyl Isethionate 16.90Water 6.00 Miscellaneous Q.S.

An inventive, flexible, porous and solid Article 5 and a comparative,flexible, porous and solid Article 6 are produced using a rotary drumdryer system comprising a feeding die, in which the feeding die ispositioned at the top of the drum dryer and is used to continuously feedthe slurry onto the drum surface. The internal flow channel of thefeeding die has a feeding width of approximately 30 cm and a feedingthickness of approximately 2 mm. The slurry is firstly pumped from thecontinuous aerator to a 50 L vessel where it was kept for a definedamount of time (i.e., aging time) to allow the bubble size to increase,and then pumped from this vessel to the feeding die. Once dried, theflexible and porous sheets so formed are peeled from the drum surfaceand placed in a plastic bag. The settings of the drum dryer-die processare shown in the following table.

TABLE 19 (DRUM DRYER-DIE PROCESS SETTINGS) Settings Article 5 Article 6Drum temperature (° C.) 100 100 Drum speed (m/min) 0.5 0.5 Aging time(min) 30 0

2) Improved Pore Structure of Solid Sheet Articles Achieved byIntroduction of an Aging Step

SEM testing is carried out according to Test 1 for Sheets 5 and 6. FIG.13A and FIG. 13B respectively show a SEM image of the top surface ofSheets 5 and 6, and the following table shows the pore structure forSheets 5 and 6 as determined according to Test 1. These data indicatethat inventive sheet articles (i.e., Article 5) has significantly largerpores on its top surface compared to comparative sheet articles (i.e.,Article 6).

TABLE 20 Top Surface Pore Structure Sample % Pore area Surface AveragePore Diameter (μm) Article 5 37.6 343.4 (Inventive) Article 6 34.7 179.9(Comparative)

3) Improved Dissolution Profile of Solid Sheet Articles Achieved byIntroduction of an Aging Step

Dissolution rates for Sheets 5 and 6 are determined according to Test 9.The following Table 21 as well as FIG. 14 shows the results of thedissolution rate testing, indicating inventive sheet article (Article 5)have significantly improved dissolution profiles compared to comparativesheet article (Article 6).

TABLE 21 Article 5 Article 6 % Dissolution Time, seconds Time, secondsRelative % 90% 129 197 53% 95% 165 261 58%

In conclusion, the introduction of an aging step (i.e., maintaining theaerated pre-mixture for a while after the aeration) in a drum dryerprocess with a feeding die also brings about a significantly improvedpore structures and thereby a significantly improved dissolutionprofile.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.” Every document cited herein, including any crossreferenced or related patent or application and any patent applicationor patent to which this application claims priority or benefit thereof,is hereby incorporated herein by reference in its entirety unlessexpressly excluded or otherwise limited. The citation of any document isnot an admission that it is prior art with respect to any inventiondisclosed or claimed herein or that it alone, or in any combination withany other reference or references, teaches, suggests or discloses anysuch invention. Further, to the extent that any meaning or definition ofa term in this document conflicts with any meaning or definition of thesame term in a document incorporated by reference, the meaning ordefinition assigned to that term in this document shall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A process for making a sheet article, comprisingthe steps of: a) preparing a wet pre-mixture comprising a water-solublepolymer and a surfactant and having a viscosity of from 1,000 cps to25,000 cps measured at 40° C. and 1 s¹; b) aerating said wet pre-mixtureto form an aerated wet pre-mixture having a density of from 0.05 to 0.5g/ml; c) aging said aerated wet pre-mixture for at least 5 min; d)forming said aged aerated wet pre-mixture into a sheet having opposingfirst and second sides; and e) drying said formed sheet for a dryingtime of from 1 minute to 60 minutes to make the sheet article.
 2. Theprocess according to claim 1, wherein the step c) is conducted for aduration from 5 min to 300 min, preferably from 5 min to 200 min, morepreferably from 10 min to 150 min.
 3. The process according to claim 1,wherein said sheet of aged aerated wet pre-mixture is dried on a heatedsurface that has a controlled surface temperature of from 70° C. to 170°C., preferably from 75° C. to 150° C., more preferably from 80° C. to140° C.; and wherein preferably said heated surface is a primary heatsource for said sheet during drying; and wherein more preferably saidheated surface is the only heat source for said sheet during drying. 4.The process according to claim 3, wherein said heated surface is theouter surface of a rotary drum dryer that preferably has an outerdiameter ranging from 0.5 meters to 10 meters, preferably from 1 meterto 5 meters, more preferably from 1.5 meters to 2 meters and is rotatedat a speed of from 0.005 rpm to 0.25 rpm, preferably from 0.05 rpm to0.2 rpm, more preferably from 0.1 rpm to 0.18 rpm, during the dryingstep.
 5. The process according to claim 4, wherein said heated surfaceis the outer surface of a heated moving belt that is preferably movingat a speed of from 0.1 m/min to 50 m/min, preferably from 0.15 m/min to20 m/min, more preferably from 0.2 m/min to 10 m/min, during the dryingstep.
 6. The process according to claim 4, wherein in the step d), saidsheet is formed by using a spinning bar that is rotating at a speed offrom 5 to 80 rpm, preferably from 6 to 60 rpm, more preferably from 8 to50 rpm, most preferably from 10 to 40 rpm.
 7. The process according toclaim 6, wherein the spinning bar is positioned so that the distancebetween the spinning bar and the outer surface of the rotary drum or theheated moving belt is from 3 mm to 15 mm, preferably from 4 mm to 12 mm,more preferably from 5 mm to 10 mm, most preferably from 6 mm to 10 mm.8. The process according to claim 4, wherein in the step d), said sheetis formed by a feeding die having a feeding speed of from 0.1 m/min to50 m/min, preferably from 0.15 m/min to 20 m/min, more preferably from0.2 m/min to 10 m/min.
 9. The process according to claim 8, wherein thefeeding die has a feeding thickness of from 0.5 mm to 10 mm, preferablyfrom 1 mm to 6 mm, more preferably from 1.5 mm to 4 mm.
 10. The processaccording to claim 1, wherein the wet pre-mixture is characterized by:(1) a solid content ranging from 15% to 70%, preferably from 20% to 50%,more preferably from 25% to 45% by weight of said wet pre-mixture; and(2) a viscosity ranging from 3,000 cps to 24,000 cps, preferably from5,000 cps to 23,000 cps, more preferably from 10,000 cps to 20,000 cpsas measured at 40° C. and 1 s⁻¹.
 11. The process according to claim 1,wherein the wet pre-mixture is preheated to a temperature of from 40° C.to 100° C., preferably from 50° C. to 95° C., more preferably from 60°C. to 90° C., most preferably from 75° C. to 85° C., before aeration;and/or wherein the wet pre-mixture is maintained at a temperature offrom 40° C. to 100° C., preferably from 50° C. to 95° C., morepreferably from 60° C. to 90° C., most preferably from 75° C. to 85° C.,during aeration; and/or wherein the aerated wet pre-mixture ismaintained at a temperature of from 10° C. to 100° C., preferably from15° C. to 70° C., more preferably from 20° C. to 50° C., most preferablyfrom 20° C. to 40° C., during aging.
 12. The process according to claim1, wherein the aerating in the step b) is accomplished by introducing agas into the wet pre-mixture by using a mechanical processing means,including but not limited to: a rotor stator mixer, a planetary mixer, apressurized mixer, a non-pressurized mixer, a batch mixer, a continuousmixer, a semi-continuous mixer, a high shear mixer, a low shear mixer, asubmerged sparger, or any combinations thereof.
 13. The processaccording to claim 1, wherein the drying in the step e) is conducted ata temperature from 70° C. to 200° C. along a heating direction thatforms a temperature gradient decreasing from the first side to theopposing second side of said formed sheet, wherein said heatingdirection is substantially opposite to the gravitational direction formore than half of the drying time.
 14. The process according to claim13, wherein the drying time is from 2 to 40 minutes, preferably from 2to 30 minutes, more preferably from 2 to 20 minutes, most preferablyfrom 2 to 15 minutes; and/or wherein the drying temperature is from 80°C. to 170° C., preferably from 90° C. to 150° C., more preferably from95° C. to 140° C.; and wherein said heating direction is substantiallyopposite to the gravitational direction for more than 55%, preferablymore than 60%, more preferably more than 75% of the drying time.
 15. Aflexible, porous, dissolvable solid sheet article comprising awater-soluble polymer and a surfactant, wherein said solid sheet articleis characterized by: (i) a thickness ranging from 0.5 mm to 4 mm; and(ii) a Percent Open Cell Content of from 80% to 100%; and (iii) anOverall Average Pore Size of from 100 μm to 2000 μm; wherein said solidsheet article has opposing top and bottom surfaces, said top surfacehaving a Surface Average Pore Diameter that is greater than 300 μm. 16.The flexible, porous, dissolvable solid sheet article of claim 15,wherein said top surface has a Surface Average Pore Diameter that isfrom 300 μm to 2 mm, preferably from 350 μm to 1.5 mm, more preferablyfrom 400 μm to 1 mm.
 17. The flexible, porous, dissolvable solid sheetarticle of claim 15, wherein said solid sheet article comprises a topregion adjacent to said top surface, a bottom region adjacent to saidbottom surface, and a middle region therebetween; wherein said top,middle, and bottom regions have the same thickness, and each of saidtop, middle and bottom regions is characterized by an Average Pore Size;and wherein the ratio of Average Pore Size in said bottom region overthat in said top region is from 0.6 to 1.5, preferably from 0.7 to 1.4,more preferably from 0.8 to 1.3, most preferably from 1 to 1.2.
 18. Theflexible, porous, dissolvable solid sheet article according to claim 15,wherein the ratio of Average Pore Size in said bottom region over thatin said middle region is from 0.5 to 1.5, preferably from 0.6 to 1.3,more preferably from 0.8 to 1.2, most preferably from 0.9 to 1.1; and/orwherein the ratio of Average Pore Size in said middle region over thatin said top region is from 1 to 1.5, preferably from 1 to 1.4, morepreferably from 1 to 1.2.
 19. The flexible, porous, dissolvable solidsheet article according to claim 15, wherein said solid sheet articlecomprises from 5% to 40%, preferably from 8% to 30%, more preferablyfrom 10% to 25%, of said water-soluble polymer by total weight of saidsolid sheet article; and wherein preferably said water-soluble polymerhas a weight average molecular weight of from 5,000 to 400,000 Daltons,more preferably from 10,000 to 300,000 Daltons, still more preferablyfrom 15,000 to 200,000 Daltons, most preferably from 20,000 to 150,000Daltons; and wherein preferably said water-soluble polymer is apolyvinyl alcohol characterized by a degree of hydrolysis ranging from40% to 100%, preferably from 50% to 95%, more preferably from 65% to92%, most preferably from 70% to 90%.
 20. The flexible, porous,dissolvable solid sheet article according to claim 19, wherein thewater-soluble polymer comprises a first water-soluble polymer having afirst weight average molecular weight and a second water-soluble polymerhaving a second weight average molecular weight, in which the firstweight average molecular weight is preferably from 5,000 to 50,000Daltons, more preferably from 10,000 to 40,000 Daltons, still morepreferably from 15,000 to 35,000 Daltons, most preferably from 20,000 to30,000 Daltons; and/or the second weight average molecular weight ispreferably from 20,000 to 400,000 Daltons, more preferably from 30,000to 300,000 Daltons, still more preferably from 40,000 to 200,000Daltons, most preferably from 50,000 to 150,000 Daltons.
 21. Theflexible, porous, dissolvable solid sheet article according to claim 15,wherein said solid sheet article comprises from 5% to 80%, preferablyfrom 10% to 70%, more preferably from 30% to 65%, of said surfactant bytotal weight of said solid sheet article; preferably, wherein saidsurfactant is selected from the group consisting of: anionicsurfactants, non-ionic surfactants, cationic surfactants, amphotericsurfactants, zwitterionic surfactants and any combinations thereof; andmore preferably, wherein said surfactant is selected from the groupconsisting of: a C₆-C₂₀ linear alkylbenzene sulfonate (LAS), a C₆-C₂₀linear or branched alkylalkoxy sulfates (AAS) having a weight averagedegree of alkoxylation ranging from 0.5 to 10, a C₆-C₂₀ linear orbranched alkylalkoxylated alcohols (AA) having a weight average degreeof alkoxylation ranging from 5 to 15, a C₆-C₂₀ linear or branched alkylsulfates (AS), alkyl sulfates, alkyl ether sulfates, alkylamphoacetatesand any combinations thereof.
 22. The flexible, porous, dissolvablesolid sheet article according to claim 15; and wherein said solid sheetarticle further comprises from 0.1% to 25%, preferably from 0.5% to 20%,more preferably from 1% to 15%, most preferably from 2% to 12%, of aplasticizer by total weight of said solid sheet article; and whereinpreferably said plasticizer is selected from the group consisting ofglycerin, ethylene glycol, polyethylene glycol, propylene glycol, andcombinations thereof; and wherein more preferably said plasticizer isglycerin.
 23. The flexible, porous, dissolvable solid sheet articleaccording to claim 15, wherein said solid sheet article is characterizedby: a Percent Open Cell Content of from 85% to 100%, preferably from 90%to 100%; and/or an Overall Average Pore Size of from 150 μm to 1000 μm,preferably from 200 μm to 600 μm; and/or an Average Cell Wall Thicknessof from 5 μm to 200 μm, preferably from 10 μm to 100 μm, more preferablyfrom 10 μm to 80 μm; and/or a final moisture content of from 0.5% to25%, preferably from 1% to 20%, more preferably from 3% to 10%, byweight of said solid sheet article; and/or a thickness of from 0.6 mm to3.5 mm, preferably from 0.7 mm to 3 mm, more preferably from 0.8 mm to 2mm, most preferably from 1 mm to 1.5 mm; and/or a basis weight of from50 grams/m² to 250 grams/m², preferably from 80 grams/m² to 220grams/m², more preferably from 100 grams/m² to 200 grams/m²; and/or adensity of from 0.05 grams/cm³ to 0.5 grams/cm³, preferably from 0.06grams/cm³ to 0.4 grams/cm³, more preferably from 0.07 grams/cm³ to 0.2grams/cm³, most preferably from 0.08 grams/cm³ to 0.15 grams/cm³; and/ora Specific Surface Area of from 0.03 m²/g to 0.25 m²/g, preferably from0.04 m²/g to 0.22 m²/g, more preferably from 0.05 m²/g to 0.2 m²/g, mostpreferably from 0.1 m²/g to 0.18